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Background and Methods Recent studies have shown that long-term survivors of acquired aplastic anemia may be at high risk for malignant diseases. We assessed the risk of cancer after aplastic anemia was treated with immunosuppression or bone marrow transplantation and sought to identify risk factors according to treatment. The study population consisted of 860 patients treated by immunosuppression and 748 patients who had received bone marrow transplants for the treatment of severe aplastic anemia. The risk of cancer was analyzed overall and according to treatment relative to the risk in the general population. In calculating relative risk, we excluded patients with myelodysplastic syndromes or acute leukemias arising less than 6 months after treatment, and solid cancers arising less than 12 months after treatment, because of a possible association with aplastic anemia itself rather than with the treatment received.
Results Forty-two malignant conditions were reported in the 860 patients who received immunosuppressive therapy: 19 cases of myelodysplastic syndrome, 15 cases of acute leukemia, 1 case of non-Hodgkin's lymphoma, and 7 solid tumors. Nine were reported in the 748 patients who received bone marrow transplants: two cases of acute leukemia and seven solid tumors. After the exclusions listed above, the overall relative risk of cancer was 5.50 (P<0.001) as compared with that in the general European population; the risk was 5.15 (P<0.001) after immunosuppressive therapy and 6.67 (P<0.001) after transplantation. The 10-year cumulative incidence rate of cancer was 18.8 percent after immunosuppressive therapy and 3.1 percent after transplantation. The risk factors for myelodysplastic syndrome or acute leukemia after immunosuppressive therapy included the addition of androgens to the immunosuppressive treatment (relative risk = 0.28), older age (relative risk = 1.03), treatment in 1982 or later, as compared with 1981 or earlier (relative risk = 3.01), splenectomy (relative risk = 3.65), and treatment with multiple courses of immunosuppression (relative risk = 2.26). Risk factors for solid tumors after bone marrow transplantation were age (relative risk = 1.11 per year) and the use of radiation as a conditioning regimen before transplantation (relative risk = 9.56); such tumors occurred only in male patients.
Conclusions Survivors of aplastic anemia are at high risk for subsequent malignant conditions. Myelodysplastic syndrome and acute leukemia tend to follow immunosuppressive therapy, whereas the incidence of solid tumors is similar after immunosuppression and after bone marrow transplantation.
Several studies3,8,9 have suggested that long-term survivors of aplastic anemia treated with immunosuppressive therapy are prone to hematologic cancers. More recent studies suggested an increased incidence of solid cancers after bone marrow transplantation for aplastic anemia10,11. To examine these complications in a large cohort of patients, we studied the cases reported to the European Bone Marrow Transplantation-Severe Aplastic Anaemia (EBMT-SAA) Working Party.
Methods
Patients' Characteristics
From July 1971 to December 1991, 1608 patients with nonconstitutional aplastic anemia who were treated at 73 institutions (see Appendix) were registered. Basic information on file on these patients includes demographic information, pretreatment biologic data, treatment characteristics, data on short-term and long-term toxicity, and vital status. By agreement among the participating centers, registration was intended to be complete, but we did not attempt to verify the completeness of the patient list. Seventy percent of the patients (n = 1122) presented with acquired idiopathic aplastic anemia. The diagnosis of acquired aplastic anemia was based on established criteria12. A list of all patients registered in the EBMT-SAA Working Party data base was sent to each contributing center, together with a questionnaire requesting information about the type of tumor each patient had, the date of its occurrence, the date of the last examination, and current status. Patients were identified by a unique patient number in the data base. The data were updated in April 1992, and all but nine centers, each with fewer than 10 patients registered, had replied by that date. No patient whose tumor occurred before the receipt of his or her initial registration information was included in the study. Two mutually exclusive therapeutic groups were studied. The first group consisted of the 860 patients treated with immunosuppressive therapy only, and the second consisted of the 748 patients who underwent bone marrow transplantation. The mean age at diagnosis was 29 years (range, 3 months to 83 years) in the immunosuppressive-therapy group and 18 years (range, 1 month to 59 years) in the transplantation group. The ratio of male to female patients was 1.3 in the immunosuppressive-therapy group and 1.6 in the transplantation group. According to international criteria,13 70 percent of the patients in the immunosuppressive-therapy group and 80 percent of those in the transplantation group were classified as having severe disease. Six hundred seventy (90 percent) of the patients who underwent bone marrow transplantation received marrow from an HLA-identical sibling donor, 14 from a twin donor, and 64 from an alternative donor. First-line immunosuppressive therapy and the conditioning regimen used before transplantation are summarized in Table 1. Prophylaxis against graft-versus-host disease consisted of methotrexate for 277 patients (37 percent), cyclosporine for 346 patients (46 percent), or both drugs for 68 patients (9 percent), as described previously14 or with slight modifications. The remaining 57 patients either received no prophylaxis (those receiving marrow from a twin) or followed other regimens.
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Follow-up began on the day immunosuppressive therapy or the process of bone marrow transplantation was begun and continued until death, the last examination, or April 1, 1992, whichever came first. The cancers observed were classified by site and histologic type according to the oncology section of the International Classification of Diseases15. The diagnoses used were those provided by the centers where patients were originally treated. No attempt was made to review the histologic material.
Three approaches were used to analyze the risk of cancer after the treatment for severe aplastic anemia. In the first, the cumulative incidence rates of cancer were calculated with Kaplan-Meier estimates. The Greenwood method was used to calculate the confidence intervals of the rates. In the second method, the excess number of cancers diagnosed after treatment for aplastic anemia was calculated as the ratio of observed cancers to those expected in the general European population. The numbers expected were calculated, country by country, with the use of cancer incidence rates specific for age, sex, and year that have been published by the International Agency for Research on Cancer16. These numbers were then pooled and compared with the number of cases observed. The numbers observed included only the cases of acute leukemia, non-Hodgkin's lymphoma, and solid tumors diagnosed, since no incidence data were available for myelodysplastic syndrome. The confidence intervals of the ratios of observed to expected cases were calculated, and the equality of the numbers observed and numbers expected was tested by assuming the Poisson distribution for observed numbers. A two-sided test was used. In these two approaches, the length of time at risk for the development of a cancer was defined as the time in months from the date immunosuppressive therapy or bone marrow transplantation was begun (even if immunosuppressive therapy was given before bone marrow transplantation) to the date of the diagnosis of the tumor, the date of the last examination, or April 1, 1992, whichever came first.
In the third method, the relation between the time of the occurrence of cancer and concomitant variables was calculated with the Cox proportional-hazards model,17 with a backward, stepwise regression. The first analysis compared the cumulative risk of cancers in the two treatment groups. The variables tested for the risk of cancer after immunosuppressive therapy were age, sex, time of treatment, heterogeneity of treatment center, cause of cancer, severity of the disease,13 need for previous therapy, type of immunosuppressive therapy used, use of a second type of immunosuppressive therapy, occurrence of paroxysmal nocturnal hemoglobinuria, and previous splenectomy. Two separate analyses were performed to assess the risk of hematologic cancer after immunosuppressive therapy. In the first one, acute leukemias and myelodysplastic syndromes were combined, whereas in the second one only myelodysplastic syndromes were considered. The variables tested for the risk of a solid tumor after bone marrow transplantation were age, sex, time of treatment, heterogeneity of treatment center, cause of cancer, severity of the disease, previous type of immunosuppressive therapy used (if any), use of radiation-based conditioning, prophylactic regimen used against graft-versus-host disease, occurrence and severity of acute and chronic graft-versus-host disease, and previous splenectomy. In both treatment groups, the potential heterogeneity of the centers was taken into account in the regression model by subgrouping the centers in which fewer than 50, 50 to 99, and 100 or more patients were registered. The time of treatment was also included in the regression model: patients treated before 1981 were compared with those treated after. An age-adjusted analysis of the cumulative risk of a solid cancer in the two treatment groups combined was performed with the same regression model in which the time of treatment and heterogeneity of center were included as covariates. To avoid any tumor synchronous with aplastic anemia but likely to be unrelated to treatment for aplastic anemia, cases of myelodysplastic syndrome and acute leukemia developing less than 6 months after treatment for aplastic anemia and solid cancers developing less than 12 months after treatment were excluded from the analysis. In Cox regression analyses, the time at risk for the development of a malignant condition was defined as above, minus 6 or 12 months as appropriate.
Patients were considered lost to follow-up if the time between the date of their last examination and April 1, 1992, exceeded 36 months. The STATA statistical package was used18.
Results
As of April 1992, the mean follow-up was 39 months (range, 1 month to 14 years) in the immunosuppressive-therapy group and 47 months (range, 1 month to 16 years) in the group that underwent bone marrow transplantation. Overall, 60 events were recorded in 51 patients (30 male and 21 female patients) (Table 2).
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A single case of non-Hodgkin's lymphoma was reported, classified as nodular, large-cell type, of intermediate grade23. Fourteen solid cancers were reported (six head and neck epidermoid carcinomas, two adenocarcinomas of the stomach, four hepatocarcinomas, and two breast cancers). Seven cases occurred after immunosuppressive therapy alone, and seven cases after bone marrow transplantation (Table 2).
The cumulative incidence of all observed cancers according to treatment group is shown in Figure 1. Overall, the 10-year cumulative incidence rate was 18.8 percent (95 percent confidence interval, 12.6 to 27.4) after immunosuppressive therapy and 3.1 percent (95 percent confidence interval, 1.6 to 6.2) after bone marrow transplantation. The 10-year cumulative incidence rates were 9.6 percent (95 percent confidence interval, 5.5 to 16.5) for myelodysplastic syndrome not followed by an acute leukemia; 6.6 percent (95 percent confidence interval, 3.6 to 11.8) and 0.4 percent (95 percent confidence interval, 0.1 to 1.8) for acute leukemia occurring after immunosuppressive therapy and bone marrow transplantation, respectively; and 2.2 percent (95 percent confidence interval, 1.1 to 4.5) and 2.9 percent (95 percent confidence interval, 1.3 to 6.2) for solid tumors occurring after immunosuppressive therapy and bone marrow transplantation, respectively.
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The ratio of cancers observed in the patients relative to those expected in the general population was 5.50 (P<0.001), for a total of 32 observed cancers (excluding the 19 cases of myelodysplastic syndrome not followed by acute leukemia) (Table 3). The overall ratio was 85 (P<0.001) for acute leukemia and 2.57 (P = 0.001) for solid tumors. When analyzed according to the type of solid tumor present, the ratio was significantly increased for head and neck cancers (P<0.001), liver carcinomas (P<0.001), and stomach adenocarcinomas (P = 0.02).
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Age-Adjusted Analysis of Cumulative Risk in the Two Groups
Three comparisons were made with the Cox model with three end points: the number of acute leukemias, myelodysplastic syndromes, and solid tumors as a whole; the number of acute leukemias; and the number of solid tumors. When all cases of cancer were considered as the end point, the risk in the immunosuppressive-therapy group relative to that in the transplantation group was 2.63 (95 percent confidence interval, 1.21 to 5.72; P = 0.01). When only cases of leukemia were considered, the relative risk was 7.57 (95 percent confidence interval, 1.72 to 33.35; P = 0.007). In contrast, no statistically significant difference between groups was observed when the number of solid tumors was considered as the end point.
Analysis of Risk Factors
In the analyses of risk factors, the time at risk for the development of a cancer was defined as in the Methods section minus 6 to 12 months as appropriate. Thus, the number of patients receiving immunosuppressive therapy who were eligible for the analysis of the risk of myelodysplastic syndrome or acute leukemia was 619, for a total of 31 events. The number of patients receiving immunosuppressive therapy who were eligible for the analysis of the risk of a solid tumor was 528, for a total of six events. The number of patients who underwent bone marrow transplantation and were eligible for the analysis of the risk of a solid tumor was 408, for a total of six events.
In multivariate analysis, five factors significantly affected the risk that myelodysplastic syndrome or acute leukemia would develop after immunosuppressive therapy: the addition of androgens to a regimen of antithymocyte globulin plus methylprednisolone (relative risk = 0.28, P = 0.02); age at diagnosis (relative risk = 1.03, P = 0.02), with age considered as a continuous variable and with the risk increasing with age; treatment in 1982 or later, as compared with 1981 or earlier (relative risk = 3.01, P = 0.02); splenectomy (relative risk = 3.65, P = 0.03); and treatment with two or more courses of immunosuppressive therapy (relative risk = 2.26, P = 0.03). When myelodysplastic syndrome was used as the end point, the same factors remained significant. In this analysis, however, splenectomy emerged as the most prognostic factor (relative risk = 5.56, P = 0.005), followed by time of treatment (relative risk = 4.11, P = 0.01), treatment with two or more courses of immunosuppressive therapy (relative risk = 2.77, P = 0.02), the addition of androgens to a regimen of antithymocyte globulin plus methylprednisolone (relative risk = 0.25, P = 0.02), and older age at diagnosis (relative risk = 1.03, P = 0.02).
In multivariate analysis, none of the factors tested were significantly related to an increased risk that solid tumors would develop after immunosuppressive therapy. In contrast, in addition to male sex (all the solid tumors developed in male patients), two factors were significantly correlated with an increased risk of solid tumors after bone marrow transplantation: age at diagnosis (relative risk = 1.11, P = 0.03), with risk increasing with age; and the use of a radiation-based conditioning regimen (relative risk = 9.56, P = 0.05).
Discussion
Our study focuses on the risk of cancer after treatment for severe acquired aplastic anemia in 1608 patients in the EBMT-SAA Working Party data base over a 20-year period. Sixty events occurred in 51 patients, leading to 10-year cumulative incidence rates of 18.8 percent and 3.1 percent after immunosuppressive therapy and bone marrow transplantation, respectively. Though malignant diseases have been reported to occur after both therapeutic options,5,6,10,11,24,25 no quantification of the excess cases of cancers observed and no multivariate analysis of risk factors have been undertaken, mainly because of the rarity of the disease.
This series includes 36 patients in whom hematologic cancers developed; most cases (34 of 36) occurred after immunosuppressive therapy, leading to a 10-year cumulative incidence rate of 9.6 percent for myelodysplastic syndrome and 6.6 percent for acute leukemia. These results are consistent with those of single-institution studies,8,9,26,27 an earlier EBMT report,4 and a study that reported five cases of acute leukemia due to monotherapy with androgens among 156 patients28. Since the criteria used to distinguish hypoplastic myelodysplastic syndrome from aplastic anemia have changed over the 20-year period of the survey, we cannot be certain that some patients in whom a hematologic cancer developed would not be classified as having hypoplastic myelodysplastic syndrome today29. In particular, cytogenetic analyses may discriminate between these two diseases in some cases30. Whether aplastic anemia is a preleukemic syndrome remains unresolved2,24,31. In contrast, acute leukemia after bone marrow transplantation is very unusual32,33 -- a result confirmed in the present study, in which only two cases were observed among 748 patients who underwent bone marrow transplantation.
The risk of acute leukemia after treatment for aplastic anemia was highly increased relative to that in the general European population, after both immunosuppressive therapy and bone marrow transplantation. Among the factors studied, older age at diagnosis, treatment in 1982 or later, treatment with multiple courses of immunosuppressive therapy, and splenectomy were found to correlate with an increased risk of hematologic cancer, and the addition of androgens to immunosuppressive therapy to a decreased risk. When the analysis was restricted to myelodysplastic syndrome, these five risk factors remained significant, with splenectomy being the most statistically significant one. In published series of patients with aplastic anemia in whom hematologic cancers developed, age was generally not analyzed, preventing any comparison with our data. Age has been shown to increase the risk of secondary acute leukemia after treatment for Hodgkin's disease34. Retreatment of patients after immunosuppressive therapy generally leads to a hematologic response in 20 to 40 percent6 -- a result that should be balanced against the increased risk of malignant hematologic complications. Myelodysplastic syndrome developed in at least three patients who relapsed and were retreated with cyclosporine, hematopoietic growth factors, or both5. Splenectomy is correlated with an increased risk of subsequent hematologic cancer9 and is a recognized risk factor for secondary acute leukemia after the treatment of Hodgkin's disease36. Finally, the time of treatment has been shown to be an independent risk factor for hematologic cancer, perhaps because myelodysplastic syndrome has recently become a more widely recognized complication of immunosuppressive therapy.
Mucosal squamous-cell carcinoma of the head and neck was the most frequently observed tumor in our series, as has been reported after renal transplantation37 but not after Hodgkin's disease38 or childhood cancer,39 in which sarcomas and adenocarcinomas are more common. Other histologic types occurring in our study included adenocarcinoma of the stomach, hepatocarcinoma, and breast carcinoma. Breast cancer has also been reported to occur in excess after Hodgkin's disease38,40. The 10-year cumulative incidence rate of solid tumors was 2.9 percent in patients who had undergone bone marrow transplantation, which is consistent with the rate reported by Witherspoon et al.11. The overall risk of a malignant solid tumor after immunosuppressive therapy and bone marrow transplantation relative to that in the general European population was increased, mainly because of an excess of head and neck cancers. Though the observed numbers of solid tumors and the mean follow-up time were similar in the two groups, the number of cases expected was four times lower in the group that underwent bone marrow transplantation than in the immunosuppressive-therapy group because of the younger age of the patients in the former group. In addition to sex, two other factors were significantly correlated with an increased risk: the use of a radiation-based conditioning regimen and older age. Our results clearly confirm that the use of radiation is a strong risk factor for the development of malignant solid tumors after bone marrow transplantation for aplastic anemia.
Though our study is based on large numbers, there are still relatively few patients with very long follow-ups and a high risk of secondary cancers. Only prolonged follow-up of large cohorts of patients and a willingness of referring physicians to report such rare cases systematically to registries will allow a more precise analysis of risk factors to be performed.
Supported by a grant (MR4-0216-S) from the European Communities.
Source Information
From the Hopital Saint Louis, Paris (G.S., E.G.); Institut Gustave Roussy, Villejuif, France (M.H.-A.); Ospedale S. Martino, Genoa, Italy (A.B.); Southmead Hospital, Bristol, United Kingdom (J.H.); Kantonsspital, Basel, Switzerland (A.T.); Huddinge University Hospital, Karolinska Institute, Huddinge, Sweden (P.L.); St. James Hospital, Dublin, Ireland (S.R.M.); Medizinische Klinik und Poliklinik, Universitat Ulm, Germany (N.F.); and Academisch Ziekenhuis, Leiden, the Netherlands (E.V.V.-K.). Members of the European Bone Marrow Transplantation-Severe Aplastic Anaemia Working Party are listed in the Appendix.
Address reprint requests to Dr. Socie at the Service de Greffe de Moelle et Unite de Recherche sur la Biologie des Cellules Souches (Laboratoire LEI-CEA/DSV), Hopital Saint Louis, 1 Ave. Claude Vellefaux, 75475 Paris CEDEX 10, France.
References
The following centers and persons participated in the European Bone Marrow Transplantation-Severe Aplastic Anaemia Working Party: University Hospital, Innsbruck, Austria (D. Niederwieser); University Hospital, Vienna, Austria (W. Hinterberger); Institut Jules Bordet, Brussels, Belgium (P. Stryckmans); University Hospital, Leuven, Belgium (M. Boogaerts); University Hospital, Budapest, Hungary (A. Poros); Rigshospitalet, Copenhagen, Denmark (V. Faber); University Hospital, Helsinki, Finland (I. Ruutu); University Hospital, Turku, Finland (A. Toivanen); Hopital Universitaire, Grenoble, France (D. Hollard); Hopital E. Herriot, Lyon, France (J.L. Touraine); Institut Jean Paoli-Irene Calmettes, Marseille, France (D. Maraninchi); Centre Hospitalier Regional, Nancy, France (P. Bordigoni); Hopital Cimiez, Nice, France (N. Gratecos); Hopital Cochin, Paris (B. Varet); Hotel-Dieu, Paris (R. Zittoun); Hopital Pitie-Salpetriere, Paris (P. Debre); Hopital Saint Louis, Paris (E. Gluckman and G. Socie); Hopital Universitaire, Pessac, France (J. Reiffers); Hopital Nord, St. Etienne, France (D. Frappaz); University Hospital, Tubingen, Germany (G. Ehninger); University Hospital, Ulm, Germany (N. Frickhofen); University Hospital, Jerusalem, Israel (S. Slavin); Ospedale di Bergamo, Bergamo, Italy (T. Barbini); Clinica S. Orsola, Bologna, Italy (S. Tura); Ospedale S. Maurizio, Bolzano, Italy (P. Coser); Ospedale Businco, Cagliari, Italy (G. Broccia); Ospedale Civile, Cuneo, Italy (Gallamini); Universita di Firenze, Florence, Italy (P. Rossi Ferrini); Istituto Gaslini, Genoa, Italy (G. Dini); Ospedale S. Martino, Genoa, Italy (A. Bacigalupo); Universita di Genova, Genoa, Italy (Ghio); Ospedale Niguarda, Milan, Italy (F. de Cataldo); Ospedale di Modena, Modena, Italy (Silingardi); Ospedale di Monza, Monza, Italy (G. Masera); Ospedale Pausillipo, Naples, Italy (Pinta); Ospedale di Nuoro, Nuoro, Italy (Gabbas); Ospedale Cevello, Palermo, Italy (S. Mirto); Policlinico S. Matteo, Pavia, Italy (G.R. Burgio); Ospedale di Pesaro, Pesaro, Italy (G. Lucarelli); Ospedale di Pescara, Pescara, Italy (G. Torlontano); Universita di Roma, Rome (F. Mandelli); Ospedale Regionale S. Giovanni, Rotondo, Italy (Carotenuto); Universita di Torino, Torino, Italy (L. Risegotti); Ospedale di Vicenza, Vicenza, Italy (Battista); St. James Hospital, Dublin, Ireland (S.R. McCann); University Hospital, Leiden, the Netherlands (J.M. Vossen and F.E. Zwann); Postgraduate School of Haematology, Barcelona, Spain (A. Granena); Huddinge Hospital, Huddinge, Sweden, (P. Ljungman); Kantonsspital, Basel, Switzerland (C. Nissen, B. Speck, A. Gratwohl, and A. Tichelli); Hopital Cantonal, Geneva (M. Jeannet); University Hospital, Zurich, Switzerland (J. Gmur); University Hospital, Ankara, Turkey (Korkut); East Birmingham Hospital, Birmingham, United Kingdom (D.W. Milligan); the Royal Infirmary, Edinburgh, Scotland (A.C. Parker); Charing Cross Hospital, London (J. Barrett); Hammersmith Hospital, London (J. Hows); Royal Free Hospital, London (S. Cleaver and H.G. Prentice); Royal Marsden Hospital, London (R. Powles); and Westminster Hospital, London (J.R. Hobbs).
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