Scholarly article on topic 'Extramedullary Relapse of Acute Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation: Different Characteristics between Acute Myelogenous Leukemia and Acute Lymphoblastic Leukemia'

Extramedullary Relapse of Acute Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation: Different Characteristics between Acute Myelogenous Leukemia and Acute Lymphoblastic Leukemia Academic research paper on "Clinical medicine"

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{"Acute leukemia" / "Acute lymphoblastic leukemia" / "Acute myelogenous leukemia" / "Allogeneic hematopoietic stem cell transplantation" / "Extramedullary relapse"}

Abstract of research paper on Clinical medicine, author of scientific article — Ling Ge, Fan Ye, Xinliang Mao, Jia Chen, Aining Sun, et al.

Abstract Extramedullary relapse (EMR) of acute leukemia (AL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a contributor to post-transplantation mortality and remains poorly understood, especially the different characteristics of EMR in patients with acute myelogenous leukemia (AML) and those with acute lymphoblastic leukemia (ALL). To investigate the incidence, risk factors, and clinical outcomes of EMR for AML and ALL, we performed a retrospective analysis of 362 patients with AL who underwent allo-HSCT at the First affiliated Hospital of Soochow University between January 2001 and March 2012. Compared with patients with AML, those with ALL had a higher incidence of EMR (12.9% versus 4.6%; P = .009). The most common site of EMR was the central nervous system, especially in the ALL group. Multivariate analyses identified the leading risk factors for EMR in the patients with AML as advanced disease status at HSCT, hyperleukocytosis at diagnosis, history of extramedullary leukemia before HSCT, and a total body irradiation–based conditioning regimen, and the top risk factors for EMR in the patients with ALL as hyperleukocytosis at diagnosis, adverse cytogenetics, and transfusion of peripheral blood stem cells. The prognosis for EMR of AL is poor, and treatment options are very limited; however, the estimated 3-year overall survival (OS) was significantly lower in patients with AML compared with those with ALL (0 versus 18.5%; P = .000). The characteristics of post–allo-HSCT EMR differed between the patients with AML and those with ALL, possibly suggesting different pathogenetic mechanisms for EMR of AML and EMR of ALL after allo-HSCT; further investigation is needed.

Academic research paper on topic "Extramedullary Relapse of Acute Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation: Different Characteristics between Acute Myelogenous Leukemia and Acute Lymphoblastic Leukemia"

Biol Blood Marrow Transplant xxx (2014) 1—8

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Extramedullary Relapse of Acute Leukemia after Allogeneic Hematopoietic Stem Cell Transplantation: Different Characteristics between Acute Myelogenous Leukemia and Acute Lymphoblastic Leukemia

Q8 Ling Ge1, Fan Ye1, Xinliang Mao 2, Jia Chen1, Aining Sun1, Xiaming Zhu1, Huiying Qiu1, Zhengming Jin1, Miao Miao1 Chengcheng Fu 1, Xiao Ma 1, Feng Chen 1, Shengli Xue 1,

American Society for Blood and Marrow Transplantation

Changgeng Ruan 1, Depei Wu 11 *, Xiaowen Tang

1 Department of Hematology, First Affiliated Hospital of Soochow University, Jiangsu Institute of Hematology, Key Laboratory of Thrombosis and Hemostasis, Ministry of Health, Suzhou, China

2 Cyrus Tang Hematology Center, Jiangsu Institute of Hematology, First Affiliated Hospital of Soochow Q1 University, Soochow University, Suzhou, China

Article history: Received 8 January 2014 Accepted 25 March 2014

Key Words: Acute leukemia Acute lymphoblastic leukemia Acute myelogenous leukemia Allogeneic hematopoietic stem cell transplantation Extramedullary relapse

ABSTRACT

Extramedullary relapse (EMR) of acute leukemia (AL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a contributor to post-transplantation mortality and remains poorly understood, especially the different characteristics of EMR in patients with acute myelogenous leukemia (AML) and those with acute lymphoblastic leukemia (ALL). To investigate the incidence, risk factors, and clinical outcomes of EMR for AML and ALL, we performed a retrospective analysis of 362 patients with AL who underwent allo-HSCT at the First affiliated Hospital of Soochow University between January 2001 and March 2012. Compared with patients with AML, those with ALL had a higher incidence of EMR (12.9% versus 4.6%; P = .009). The most common site of EMR was the central nervous system, especially in the ALL group. Multivariate analyses identified the leading risk factors for EMR in the patients with AML as advanced disease status at HSCT, hyperleukocytosis at diagnosis, history of extramedullary leukemia before HSCT, and a total body irradiation—based conditioning regimen, and the top risk factors for EMR in the patients with ALL as hyperleukocytosis at diagnosis, adverse cytogenetics, and transfusion of peripheral blood stem cells. The prognosis for EMR of AL is poor, and treatment options are very limited; however, the estimated 3-year overall survival (OS) was significantly lower in patients with AML compared with those with ALL (0 versus 18.5%; P = .000). The characteristics of post—allo-HSCT EMR differed between the patients with AML and those with ALL, possibly suggesting different pathogenetic mechanisms for EMR of AML and EMR of ALL after allo-HSCT; further investigation is needed, however.

© 2014 American Society for Blood and Marrow Transplantation.

INTRODUCTION

Although allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment for patients with acute leukemia (AL), relapse remains the most frequent cause of treatment failure and mortality. In particular, a significant rate of extramedullary relapse (EMR) after allo-HSCT has been reported [1-6], with a poor prognosis. Although risk factors for EMR have been described in patients with acute myelogenous leukemia (AML), few studies have compared the different characteristics of EMR in patients with AML and patients with acute lymphoblastic leukemia (ALL) in the post-HSCT setting.

In an effort to better understand post-HSCT EMR, we performed a retrospective analysis on 362 patients with AL who underwent allo-HSCT in the First affiliated Hospital of Soochow University between January 2001 and March 2012.

Financial disclosure: See Acknowledgments on page 7. * Correspondence and reprint requests: Xiaowen Tang and Depei Wu, Department of Hematology, First Affiliated Hospital of Soochow University, Jiangsu Institute of Hematology, 188 Shizi Rd, Suzhou 215006, PR China.

E-mail addresses: wudepei@medmail.com (D. Wu), xwtang1020@ 163.com (X. Tang).

We studied the incidence, risk factors, treatments, outcomes, and mechanisms of post-HSCT EMR in patients with ALL and AML.

PATIENTS AND METHODS Patients

A total of 362 patients with AL who underwent allo-HSCT in our institution between January 2001 and March 2012 were enrolled in this retrospective study, including 208 patients with AML, 147 with ALL, and 7 with acute mixed lineage leukemia (AMLL). These patients included 204 males and 158 females, with a median age of 32 years (range, 3 to 63 years). The graft donor sources for allo-HSCT were unrelated in 27.1% of cases, sibling in 58.3%, and haploidentical in 14.6%; 79.6% of the transplants were HLA-matched. Stem cell sources included bone marrow (BM) in 45.6%, peripheral blood (PB) stem cells (PBSCs) in 36.5%, and BM plus PBSCs in 17.9%. In this study, 260 patients (71.8%) received a modified busulfan (Bu)/cyclo-phosphamide (Cy) conditioning regimen, 89 (24.6%) received a total body irradiation (TBI)/Cy regimen, and 13 (3.6%) received a nonmyeloablative conditioning regimen. Patient characteristics are summarized in Table 1. Patients were treated according to clinical protocols approved by the Institutional Review Board and/or institutional care practice guidelines of Soo-chow University.

Conditioning Regimen

Of the 362 patients, 260 patients received a modified Bu/Cy regimen (Me-CCNU 250 mg/m2/day on day -10, Ara-C 4 g/m2/day on days -9 to -8, Bu 0.8 to 1 mg/kg/6 hours on days -7 to -5, and Cy 1.8 g/m2/day on days -4

80 81 82

99 100 101 102

110 111 112

120 121 122

1083-8791/$ — see front matter © 2014 American Society for Blood and Marrow Transplantation. http://dx.doi.org/10.1016/j.bbmt.2014.03.030

Table 1

Clinical Characteristics of 362 Patients with AL Post-HSCT

Characteristic AML ALL AMLL

(n = 208) (n = 147) (n = 7)

Age, yr, median (range) 35 (3-63) 25 (4-57) 26 (20-54)

Sex, n

Male 116 83 5

Female 92 64 2

Hyperleukocytosis at diagnosis, n 66 52 1

EM leukemia before HSCT, n 14 13 0

High cytogenetic risk, n 20 65 3

Disease status at HSCT, n

CR1 163 110 5

>CR2 23 36 0

NR 22 1 2

Conditioning regimen, n

Bu/Cy 185 72 3

TBI/Cy 11 74 4

NST 12 1 0

Stem cell source, n

BM 100 62 3

PB 72 58 2

BM + PB 36 27 2

Donor type, n

Sibling 142 66 3

URD 43 53 2

Haploidentical 23 28 2

aGVHD grade, n

I-II 67 51 5

III-IV 13 9 0

cGVHD, n 61 38 3

NR indicates no remission; NST, nonmyeloablative conditioning regimen;

URD, unrelated donor.

to -3) as a preparative regimen, and 89 patients received a TBI/Cy regimen

consisting of fractionated TBI 12 Gy on days -8 to -6, Ara-C 2 g/m2/day on

day -5, and Cy 1.8 g/m2/day on days -4 to -3. Thirteen patients received nonmyeloablative Bu/fludarabine (Flu) conditioning regimen (Bu 0.8 mg/kg/

6 hour on days -6 to -5, Flu 30 mg/m2/day on days -7 to -2, and Ara-C 0.5 g/m2/day on days -8 to -4).

Graft-Versus-Host Disease Prophylaxis

Acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD) were classified according to the criteria proposed by Przepiorka et al. [7] and Sullivan [8]. GVHD prophylaxis included cyclosporine A with short-term methotrexate for related identical transplantation and cyclosporine A, methotrexate, mycophenolate mofetil, and human antithymocyte globulin for unrelated and haploidentical transplantation. The haploidentical grafts were non—T cell depleted.

Central Nervous System Relapse Prophylaxis after Transplantation

Prophylactic intrathecal chemotherapy (with methotrexate or cytosine arabinoside and dexamethasone) each month for 6 months was

administered to all patients with ALL and high-risk AML in the first year after allo-HSCT.

Definitions and Statistical Analysis

EMR included isolated EMR and EMR with concurrent bone marrow relapse (BMR); isolated EMR was defined as EMR without concurrent BMR. EMR was diagnosed in most cases by magnetic resonance imaging, computed tomography, or positron emission tomography. Histological confirmation was performed whenever possible. Central nervous system (CNS) relapse was diagnosed when leukemic cells were identified in the cerebrospinal fluid. Isolated CNS relapse was defined as CNS relapse without any other sites of leukemia relapse. Clinical remission (CR) was defined as <5% blasts in the BM with normal complete blood count values. High-risk cytogenetics was defined as complex karyotype, 5q-, monosomy 7/7q-, and/or FLT-3—positive for AML and AMLL gene rearrangement and/or Philadelphia chromosome in ALL. Hyperleukocytosis was defined as a peripheral WBC count >50 x 109/L at diagnosis of AML, B lymphoblastic leukemia as >30 x 109/L, and T lymphoblastic leukemia as >100 x 109/L.

The cumulative incidence estimation for leukemia relapse was determined by treating death as a competing risk and was compared using the method of Gray [9]. Overall survival (OS) was calculated from the date of relapse post-transplantation to death or last follow-up for censored cases, and was estimated using the Kaplan-Meier method and compared with a log-rank test. Continuous variables were compared with the Mann-Whitney test, and categorical variables were compared with the chi-square test. A comprehensive multivariate analysis of risk factors for relapse was estimated using the Cox proportional hazards regression model. All statistical analyses were performed with SPSS version 16.0 (SPSS Inc, Chicago, IL) and R version 2.15.1 (R Project for Statistical Computing, Vienna, Austria).

RESULTS

Patient Characteristics

We retrospectively analyzed a consecutive series of 362 patients with AL who underwent allo-HSCT in our single institution. Of these 362 patients, 163 of 208 with AML, 110 of 147 with ALL, and 5 of 7 with AMLL were in first CR status (CR1) at the time of allo-HSCT. After transplantation, 40.1% patients experienced aGVHD, including 34.0% with mild (grade I-II) and 6.1% with severe (grade III-IV) aGVHD, and 28.2% patients developed cGVHD. After a follow-up ranging from 1 month to 139 months (median, 17 months), 90 patients (24.9%) developed either EMR or BMR; 64 of these relapsed patients had isolated BMR only, 11 had isolated EMR, and 15 had EMR with concurrent BMR.

Incidence and Characteristics of EMR in AL

The estimated 10-year cumulative incidence of overall relapse post—allo-HSCT was 27%. That of EMR was 7.9%, with 3.1% of patients experiencing isolated EMR. Compared with patients with AML, those with ALL had a higher estimated 10-year cumulative incidence of EMR (12.9% versus 4.6%; P = .009) (Figure 1).

Figure 1. (A) Cumulative incidence of EMR after allo-HSCT for AL. EMR with or without BMR (dotted line), 7.9% (n = 26); isolated EMR (solid line), 3.1% (n = 11); EMR with concurrent BMR (dashed line), 4.7% (n = 15). (B) Cumulative incidence of EMR after HSCT for AML versus ALL (4.6% versus 12.9%; P = .009).

260 261 262

280 281 282

Twenty-six of the 362 patients experienced EMR after allo-HSCT, including 11 with isolated EMR and 15 with EMR and concurrent BMR. Of these latter 15 patients, 6 who initially had EMR later developed BMR, 4 with BMR later developed EMR, and the remaining 5 developed EMR and BMR almost simultaneously. In our center, the median time to BMR post-HSCT was 5 months (range, 1 to 60 months), and the median time to EMR was 4 months (range, 1 to 38 months; P = .879). Involved extramedullary (EM) sites involved included the CNS, testis, skin, soft tissue, bone, lymph nodes, nasopharynx, and peritoneum. Multifocal involvement at EMR was observed in 5 of 26 patients (19.2%). CNS relapse (n = 18) was the most common type of EMR, with a cumulative incidence of 5.4%, whereas the cumulative incidence of isolated CNS relapse was 2.5%.

Among the 26 patients who developed EMR, 5 had a history of EM leukemia before undergoing allo-HSCT, all of whom relapsed at the same site as in the previous leukemia. Ten patients had mild aGVHD (grade I-II), 3 had severe aGVHD (grade III-IV), and 3 developed cGVHD before the onset of EMR. Characteristics of the 11 patients who had isolated EMR and the 15 patients who had EMR with concurrent BMR are presented in Tables 2 and 3.

Risk Factors for Overall Relapse and EMR in AL

We analyzed the variables of interest by Cox proportional hazard modeling to identify risk factors for AL relapse, including age, sex, disease type, donor type, stem cell source, hyperleukocytosis at diagnosis, cytogenetic risk, disease status at HSCT, HLA mismatch, conditioning regimen, EM leukemia before HSCT, aGVHD, and cGVHD. The results of our univariate and multivariate analyses are summarized in Tables 4 and 5.

In terms of overall relapse, our multivariate analyses showed that patients with high-risk cytogenetics, advanced disease status, TBI-based conditioning regimen, without cGVHD, and male sex were more likely to relapse (Table 4). The multivariate analyses also revealed a higher rate of EMR in patients with high-risk cytogenetics, advanced disease Q2 status, and male sex (relative risk [RR] = 3.860, P = .002; RR = 6.663, P = .003; and RR = 2.844, P = .038, respectively). A history of EM leukemia before undergoing HSCT and hyperleukocytosis at diagnosis also correlated with an increased risk of EMR (RR = 3.011; P = .038 and RR = 3.382; P = .004, respectively). Meanwhile, patients who received PBSC grafts were more likely to develop EMR (RR = 5.495; P = .002) (Table 5).

Table 2

Characteristics of Patients with AL Who Developed Isolated EMR after HSCT

To identify differences in pathogenesis between BMR and EMR, we performed further analyses with separate consideration of isolated BMR. Patients with advanced disease status had a higher frequency of BMR, and also were more likely to develop EMR. Multivariate analyses also revealed that the patients without cGVHD were more likely to experience BMR (RR = 5.907; P = .00); however, there was no significant difference in the incidence of EMR between patients with cGVHD and those without cGVHD. In addition, the incidence of BMR was higher in patients who received a TBI-based conditioning regimen or nonmyeloablative conditioning regimen compared with patients who received a Bu-containing regimen (RR = 2.100; P = .012 versus RR = 3.159; P = .031) (Table 5).

Differences in Risk Factors for EMR in AML and ALL

To identify differences in the pathogenesis of EMR between patients with AML and those with ALL, we performed further multivariate analyses with these 2 groups of patients separately. We found that in the patients with AML, advanced disease status, a history of EM leukemia before HSCT, use of a TBI-based conditioning regimen, and hyper-leukocytosis at diagnosis were associated with a higher frequency of EMR (RR = 16.264, P = .001 ; RR = 10.416, P = .011; RR = 10.455, P = .035; and RR = 4.699, P = .041, respectively), whereas in the patients with ALL, the top risk factors for EMR were receipt of PBSC grafts, hyperleukocytosis at diagnosis, and high-risk cytogenetics (RR = 6.015, P = .007; RR = 2.996, P = .032; and RR = 2.889, P = .042, respectively) (Table 6).

Postrelapse Treatment and Clinical Outcomes in AL

Four patients refused any treatment and died of relapse. The remaining 22 patients who experienced EMR with or without BMR received various treatment modalities. Nine patients developed isolated CNS relapse and were treated with intrathecal chemotherapy and/or cranial irradiation. One patient who experienced EMR in both the CNS and peritoneum received local chemotherapy, and another patient who developed EMR in lymph nodes was treated with chemotherapy and donor lymphocyte infusion (DLI); however, both patients died of progressive disease. Eight patients received chemotherapy, followed by local irradiation and DLI; 7 of these patients achieved CR, and 2 were still surviving as of the date of this report. The other 5 patients died of GVHD, leukemia recurrence, or CNS relapse. Two patients received chemotherapy and local irradiation, and both died

Patient Sex Age, Disease Disease EM Leukemia Donor Type Stem Cell HLA Relapse Site GVHD before Results Direct

yr Status at HSCT before HSCT Source Match Relapse Cause of Death

1 F 31 ALL CR1 No URD PB Yes CNS cGVHD Alive

2 M 22 ALL CR1 No URD PB Yes CNS aGVHD grade I Dead Infection

3 M 36 ALL CR1 No URD PB Yes CNS No Alive

4 F 22 ALL CR2 No Haploidentical PB No CNS aGVHD grade I Dead Relapse

5 M 48 ALL CR2 No Sibling PB Yes CNS aGVHD grade III and cGVHD Alive

6 M 10 ALL CR3 CNS Haploidentical BM + PB No CNS aGVHD grade IV Alive

7 M 44 ALL CR4 No Sibling PB Yes CNS No Dead Infection

8 F 35 ALL CR1 No Sibling BM + PB Yes CNS, peritoneum aGVHD grade I Dead Relapse

9 M 18 ALL CR2 Lymph nodes URD PB Yes Lymph nodes No Dead Relapse

10 M 44 AML CR1 No Sibling BM Yes CNS No Dead Relapse

11 M 29 AML CR2 CNS Haploidentical PB No CNS No Dead Relapse

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from leukemia recurrence. The remaining patient was 452

treated with supportive care and died of progressive disease. 453

In general, the estimated 3-year OS postrelapse was 454

better in patients with isolated EMR than in patients with 455

BMR only and those with EMR with concurrent BMR, but the 456

difference was not statistically significant (18.2% versus 457

12.0% versus 8.0%; P = .206) (Figure 2). Although the median 458

OS postrelapse was 9 months versus 4 months versus 459

4 months, these differences were not significance either 460

(P = .099). However, the estimated 3-year OS in these pa- 461

tients with EMR was significantly lower in those with AML 462

compared with those with ALL (0 versus 18.5%; P = .00). 463

DISCUSSION 465

EMR after allo-HSCT is relatively rare and not well stud- 466

ied. Although most previous studies reported on patients 467

with AML, there are too little data comparing characteristics 468

of EMR between patients with AML and patients with ALL. To 469

our knowledge, this is the first report to examine the dif- 470

ferences in EMR occurring after allo-HSCT in patients with 471

AML and those with ALL. We found that significant differ- 472

ences between the 2 groups of patients. 473

The incidence of EMR after allo-HSCT varies among 474

transplantation centers, ranging from 6% to 20% in single- 475

institution reports [5,6,10-12]; however, in a retrospective 476

European Group for Blood and Marrow Transplantation 477

(EBMT) survey, the incidence of post-HSCT EMR was only 478

0.65% in patients with AML [1]. The lower incidence of EMR 479

found in that multicenter study may be related to under- 480

reporting in retrospective registry data, as well as to the 481

greater number of patients reported in recent series owing to 482

longer follow-up, longer survival, and generally improved 483

outcomes of HSCT [4]. In general, the incidence of EMR is 484

higher in patients with ALL compared with those with AML 485

[4-6]. In our center, the estimated 10-year cumulative inci- 486

dence of overall post-HSCT relapse in patients with AL was 487 27%; that of EMR was 7.9%, with 3.1% of patients experiencing Q3 488

isolated EMR. The incidence of EMR was 12.9% in patients 489

with ALL and 4.6% in those with AML (P = .009). 490

Historical risk factors for EMR after HSCT include Phila- 491

delphia chromosome—positive AL, AML subtype M4/M5, age 492

<18 years at diagnosis, EM leukemia before HSCT, adverse 493

cytogenetics, relapse/refractory disease at transplantation, 494

Bu/Cy preconditioning, and CD56 and T cell marker expres- 495

sion [4,6,13,14]. In the present study, identified risk factors 496

included EM leukemia before HSCT, adverse cytogenetics, 497

and relapse/refractory disease at transplantation, consistent 498

with previous studies [4,6,13]; however, AML subtype M4/ 499

M5 and Bu/Cy preconditioning were not risk factors in our 500

study cohort. In addition, we identified male sex, hyper- 501

leukocytosis at diagnosis, a TBI-based conditioning regimen, 502

and transfusion of PBSCs as risk factors for EMR. These 503

findings have not been reported previously in the post-HSCT 504

setting; probable reasons for this include the following: 505

1. The incidence of EMR was high in our male patients 507 owing to the relatively high rate of EMR with a testis 508 leukemia subtype in our cohort (5 of 26). 509

2. Hyperleukocytosis has been identified as a risk 510 factor for CNS involvement, but not in the post- 511 transplantation setting [15]; we also found it corre- 512 lated with an increased risk of EMR after allo-HSCT. 513 Patients with hyperleukocytosis had a high tumor 514 burden, which facilitates the infiltration of tumor cells 515 to EM sites. 516

L. Ge et al. / Biol Blood Marrow Transplant xxx (2014) 1-8

Table 4

Univariate and Multivariate Analyses of Risk Factors for Overall Relapse in Patients with AL (n = 90)

Factor Univariate RR (95% CI) P Value Multivariate RR (95% CI) P Value

Sex, male/female 1.826 (1.168-2.853) .008 1.696 (1.082-2.657) .021

Age, <18 yr/>18 yr 1.565 (0.960-2.551) .072

Disease

AML 1.000

ALL 1.756 (1.154-2.672) .009

AMLL 1.598 (0.386-6.613) .518

Donor type

Sibling 1.000

URD 1.522 (0.942-2.459) .086

Haploidentical 2.361 (1.375-4.052) .002

HLA mismatch/match 1.732 (1.084-2.767) .022

Stem cell source

BM 1.000

PB 1.302 (0.817-2.077) .267

BM + PB 1.376 (0.791-2.393) .258

Hyperleukocytosis at diagnosis, yes/no 1.223 (0.799-1.873) .354

Cytogenetic risk, high/intermediate-low 2.190 (1.428-3.357) .000 1.704 (1.054-2.755) .030

Disease status at HSCT

CR1 1.000 1.000

>CR2 2.621 (1.605-4.282) .000 1.838 (1.087-3.110) .023

NR 5.140 (2.844-9.289) .000 7.123 (3.855-13.163) .000

EM leukemia before HSCT, yes/no 1.617 (0.812-3.220) .172

Conditioning regimen

Bu/Cy 1.000 1.000

TBI/Cy 2.147 (1.384-3.329) .001 1.84 16(1.112-3.064) .018

NST 1.686 (0.610-4.658) .314 2.262 (0.806-6.349) .121

aGVHD, no/yes 0.857 (0.564-1.303) .471

cGVHD, no/yes 4.547 (2.282-9.059) .000 5.127 (2.551-10.304) .000

3. There are paradoxical results from previous studies compared with TBI-containing regimens [14]. This

regarding pretransplantation conditioning regimens. result may be related to the low plasma levels of Bu

One retrospective study found a higher incidence of achieved in some patients [16]; however, other, more

isolated EMR associated with 1 Bu/Cy regimens controversial results failed to show such a difference

Table 5

Univariate and Multivariate Analyses of Risk Factors for EMR (n = 26) and BMR (n = 64) in Patients with AL

Factor EMR BMR

Univariate RR (95% CI) P Value Multivariate RR P Value Univariate RR P Value Multivariate RR P Value

(95% CI) (95% CI) (95% CI)

Sex, male/female 3.486 (1.314-9.250) .012 2.844 (1.060-7.631) .038 1.543 (0.926-2.572) .096

Age, <18/>18 yr 2.224 (o.967-5.117) .060 1.434 (0.780-2.636) .247

Disease

AML 1.000 1.000

ALL 2.911 (1.296-6.539) .010 1.509 (0.916-2.484) .106

AMLL 0.000 (0.000-) .977 2.005 (0.480-8.376) .340

Donor type

Sibling 1.000 1.000

URD 2.464 (1.025-5.926) .044 1.249 (0.697-2.236) .455

Haploidentical 3.236(1.170-8.950) .024 2.098 (1.105-3.983) .024

HLA mismatch/match) 1.735 (0.727-4.140) .214 1.737 (0.996-3.029) .052

Stem cell source

BM 1.000 1.000

PB 4.425 (1.605-12.199) .004 5.495 (1.880-16.062) .002 0.855 (0.484-1.510) .589

BM + PB 3.271 (0.998-10.719) .050 2.583 (0.752-8.870) .132 1.120 (0.588-2.135) .730

Hyperleukocytosis at 2.394(1.107-5.176) .027 3.382 (1.484-7.707) .004 0.961 (0.566-1.630) .881

diagnosis, yes/no

Cytogenetic risk, high/ 2.999 (1.385-6.495) .005 3.860 (1.647-9.045) .002 2.013 (1.201-3.375) .008

intermediate-low

Disease status at HSCT

CR1 1.000 1.000 1.000

>CR2 2.770(1.126-6.813) .026 1.154 (0.431-3.087) .775 2.598 (1.447-4.664) .001 2.052 (1.098-3.835) .024

NR 4.451 (1.467-13.505) .008 6.663 (1.923-23.085) .003 5.488 (2.728-11.043) .000 7.387 (3.593-15.189) .000

EM leukemia before 3.427 (1.291-9.093) .013 3.011 (1.064-8.521) .038 1.029 (0.374-2.833) .955

HSCT, yes/no

Conditioning regimen

Bu 1.000 1.000 1.000

TBI 2.645 (1.210-5.780) .015 1.959 (1.151-3.334) .013 2.100(1.179-3.739) .012

NST 0.000 (0.000) .979 2.247 (0.802-6.292) .123 3.159(1.114-8.956) .031

aGVHD, no/yes 0.635 (0.294-1.371) .248 0.958 (0.580-1.584) .868

cGVHD, no/yes 3.694 (1.108-12.320) .033 5.085 (2.193-11.791) .000 5.907 (2.531-13.784) .000

600 601 602

610 611 612

620 621 622

Table 6

Characteristics of Patients with AML and Patients with ALL

Characteristics EMR in AML (n = 9) EMR in ALL (n = 17) P Value

Cumulative incidence, % 4.60 12.90 .009

EMR site, n*

CNS 5 13 .382

Testis 2 3 1.000

Skin/soft tissue 3 1 .104

Bone 1 1 1.000

Lymph nodes 0 1 1.000

Nasopharynx 0 1 1.000

Peritoneum 0 1 1.000

EM leukemia before HSCT, n 2 3 1.000

Risk factorsy Hyperleukocytosis at diagnosis (RR = 4.699; P = .041) Advanced disease status (RR = 16.264; P = .001) EM leukemia before HSCT (RR = 10.416; P = .011) TBI-based conditioning regimen (RR = 10.455; P = .035) Hyperleukocytosis at diagnosis (RR = 2.996; P = .032) High-risk cytogenetics (RR = 2.889; P = .042) PB stem cell source (RR = 6.015; P = .007)

Type of therapy, n

Local 2 8 .399

Systemic 4 7 1.000

None 3 2 .302

Estimated 3-yr OS, % 0 18.50 .000

* Five of 26 patients (19%) presented with extramedullary disease in multiple sites.

y The variables were analyzed by Cox proportional hazard modeling to identify the risk factors for relapse, including age, sex, donor type, stem cell source, hyperleukocytosis at diagnosis, cytogenetic risk, disease status at HSCT, HLA mismatch, conditioning regimen, EM leukemia before HSCT, aGVHD and cGVHD,

at transplantation, 2 patients were in CR2 or greater (>CR2) at transplantation, and 1 patient had adverse cytogenetics.

4. Transplantation of PBSCs was identified as a risk factor for EMR. A possible explanation for this may be the higher rate of >CR2/refractory disease status at the time of transplantation in the patients who received PBSC grafts compared with those who received BM grafts (28.8% versus 15.1%; P = .004). Another possible explanation is that transfusion of PBSCs may be related to the presence of a graft-versus-leukemia (GVL) effect that did not protect EM sites after allo-HSCT. The increased incidence of GVHD in patients with EMR implies that GVL surveillance preferentially maintains remission in the BM while allowing leukemic cells in peripheral tissues to evade immune surveillance [13]. Furthermore, we identified transfusion of PBSCs as a independent risk factor for EMR in patients with ALL, but not in those with AML, suggesting that the GVL effect may be less effective at EM sites in ALL. This may be related to the induction of T cell anergy by ALL cells [19], inadequate expression of important cos-timulatory molecules or adhesion molecules [20,21], or ALL resistance to killing by natural killer cells [22]. Previous research also has shown that the GVL effect may be less effective at EM sites in patients with AML. Patients with EMR are more likely than those with BMR to have preceding aGVHD or cGVHD [10], a high incidence of EMR after immunomodulation (eg, DLI)or Q4 a second HSCT [23,24]. The patient heterogeneity and small sample size in a single transplantation center preclude drawing conclusions regarding the association of EMR and these risk factors; multicenter studies with larger numbers of patients are needed.

In the present study, the development of cGVHD was protective against relapse in the BM, but this protective effect did not extend to EM sites. Multivariate analyses showed that the patients without cGVHD were more likely to experience

ALL with or without the Philadelphia chromosome, and AML subtype M4/M5.

[10,17]. Oshima et al. [18] reported a higher incidence of CNS relapse in patients who received TBI-containing preconditioning, possibly because a significantly higher proportion of patients with CNS leukemia received such a regimen compared with those without CNS leukemia (81.5% versus 57.9%; P < .001). The role of conditioning regimen in preventing EMR has not been evaluated precisely. In our study, use of a TBI-containing regimen was associated with a higher incidence of EMR compared with use of a Bu/Cy regimen in the patients with AML, but not in those with ALL. This difference may be related to the fact that all 11 patients with AML who received a TBI-containing regimen were high-risk patients; 5 had a history of EM leukemia before HSCT, 3 patients were not in remission

Figure 2. Estimated 3-year OS for patients with AL relapse post-HSCT. Isolated EMR (solid line), 18.2%; isolated BMR (dashed line), 12.0%; EMR with concurrent BMR (dotted line), 8.0%; P = .206.

BMR. This finding suggests that the pathogenesis of EMR differs from that of BMR and identifies the EM sites as potential sanctuary sites for leukemia cells, possibly because of decreased expression of HLA minor histocompatibility antigens and adhesion molecules [25].

To date, there are no standardized therapeutic strategies for EMR. Generally, some combination of systemic and local therapy should be considered, given that local therapy alone often results in subsequent systemic relapse. Local therapy includes surgical excision, intrathecal injection, and/or radiation, and systemic therapy involves immunotherapy with chemotherapy, DLI, and second allo-HSCT. The optimal therapeutic strategy remains controversial, however. Recent studies have reported good treatment response with some immune-targeting drugs, including gemtuzumab ozogami-cin [26], a recombinant humanized monoclonal antibody that targets the CD33 antigen, which is expressed in >90% of leukemic cells. Sorafenib, a multikinase inhibitor, has significant activity against FLT3-ITD+ blasts in vitro and demonstrated encouraging clinical results as a single agent [27] and in combination with chemotherapy [28] for patients with AML and the FLT3-ITD mutation. Either agent may be an effective therapeutic choice for EMR after allo-HSCT [29,30]. Recently, hypomethylating agents, such as 5-azacitidine and decitabine, were successfully used in the salvage treatment of patients with AML who relapsed or experienced EMR after allo-HSCT [31-33]. It was hypothesized that hypomethylating agents are directly cytotoxic and also might increase the GVL effect by inducing leukemic cell differentiation and expression of HLA-DR to enhance the effects of DLI given concomitantly [33,34].

Owing to a lack of effective treatments, the prognosis for EMR after allo-HSCT is poor. Generally, patients with isolated EMR have a better prognosis than those with BMR [10]. In the UK Medical Research Council's UKALL12/ECOG 2993 study [35], analysis of outcomes in 609 adults with recurring ALL revealed a better 5-year OS in patients with EMR compared with patients with BMR and those with BMR and CNS relapse (14% versus 6% versus 0; P = .004). The Children's Oncology Group CCG-1961 study [36] reported obvious differences in the 3-year OS of childhood ALL in patients with BMR (with or without EMR), those with isolated CNS EMR, and those with other isolated EMR (29.7% versus 52.2% versus 68.2%; P < .0001, log-rank test). In the ALL-REZ BFM 90 trial [37], multivariate Cox regression analysis identified the site of relapse as an independent predictor for event-free survival (RR for subsequent event at an isolated EM site versus combined and isolated BM sites of relapse of 1, 1.7, and 2.3, respectively; P < .001). In the present study, in the post-HSCT setting, we also found a trend toward better prognosis in patients with isolated EMR compared with patients with BMR or systemic relapse (18.2% versus 12.0% versus 8.0%; P = .206). In addition, our patients with ALL had a significantly higher estimated 3-year OS compared with those with AML, possibly related to the higher proportion of isolated EMR in the patients with ALL. Thus, treatment should focus on preventing systemic relapse [13].

In conclusion, our results reported here demonstrate that EMR after allo-HSCT poses a significant challenge for transplantation physicians. Our patients with ALL had a higher cumulative incidence of EMR compared with those with AML. CNS relapse is the most common subtype of EMR. Patients with high-risk cytogenetics, advanced disease status, history of EM leukemia before allo-HSCT, hyperleukocytosis at diagnosis, receipt of PBSCs blood stem cell, and male are at

increased risk for EMR. These patients should be closely evaluated for early evidence of EMR. 18F-FDG-PET/CT may be Q6 a useful tool for this purpose [38]. Prophylactic intrathecal chemotherapy [39] and low-dose azacitidine or decitabine administered after allo-HSCT [33,40] may reduce the rate of recurrence. The prognosis for EMR after allo-HSCT is poor, and efficacious treatment strategies are lacking. In addition to an early diagnosis with new modalities, clinical studies using new agents that may offer systemic activity while preserving the GVL effect are warranted in an effort to improve clinical outcomes. Considering the limitations of this study and previous related studies, including single institution experience, small sample size of patients with EMR, and patient heterogeneity, future studies with larger numbers of patients are warranted to further define the incidence, risk factors, and appropriate therapeutic strategies for EMR after allo-HSCT.

ACKNOWLEDGMENTS

Financial disclosure: This work was supported by National Natural Science Foundation of China (Grant 81270645), the Natural Science Foundation of Jiangsu Province (Grant BK2012627), the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (Grant 11KJB320015), the Priority Academic Program Development of Jiangsu Higher Education Institutions, Jiangsu Provincial Health Office (Grant H201125), the Jiangsu Province Key Medical Center (Grant ZX201102), and the National Public Health Research Foundation (Grant 201202017). Q7

Conflict of interest statement: There are no conflicts of interest to report.

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