Therapeutic targeting of preleukemia cells in a mouse model of NPM1 mutant acute myeloid leukemia

The initiating mutations that contribute to cancer development are sometimes present in premalignant cells. Whether therapies targeting these mutations can eradicate premalignant cells is unclear. Acute myeloid leukemia (AML) is an attractive system for investigating the effect of preventative treatment because this disease is often preceded by a premalignant state (clonal hematopoiesis or myelodysplastic syndrome). In Npm1c/Dnmt3a mutant knock-in mice, a model of AML development, leukemia is preceded by a period of extended myeloid progenitor cell proliferation and self-renewal. We found that this self-renewal can be reversed by oral administration of a small molecule (VTP-50469) that targets the MLL1-Menin chromatin complex. These preclinical results support the hypothesis that individuals at high risk of developing AML might benefit from targeted epigenetic therapy in a preventative setting.

Unusual extramedullary recurrences and breast relapse despite hepatic GVHD after allografting in Ph+-ALL

Extramedullary recurrences with or without bone marrow involvement are reported in up to a half of leukemic relapses after BMT. Our report describes a case of an extramedullary recurrence and breast relapse after second-allografting in a female patient with Ph+-acute lymphoblastic leukemia (ALL), occurring when there was active hepatic GHVD. This case illustrates the complex relationship between graft-versus-host disease (GVHD) and graft-versus-leukemia since she had no evidence of leukemia in her marrow demonstrating 100% full-donor chimerism while she had ALL relapse in her breast.

[Myelodysplastic syndromes: preleukemic syndromes]

The myelodysplastic syndromes (MDS) are a heterogeneous group of disorders characterized by peripheral blood cytopenias with a hypercellular bone marrow exhibiting dyspoiesis. The predominant in elderly patients are associated with a high risk of progression to acute myelogenous leukemia. The etiology of MDS is unknown in most cases. About 10% of MDSs are secondary. MDS are classified by the French American British (FAB) classification into five subgroups. The incidence of the disorders is difficult to estimate but it seems to be increasing. Clonal cytogenetic aberrations are found in 30 to 50% of de novo MDS. The only currative treatment for MDS is allogeneic bone marrow transplantation.

A fludarabine-based protocol for bone marrow transplantation in Fanconi's anemia

Allogeneic bone marrow transplantation (BMT) is an effective therapy for Fanconi's anemia (FA). However, mortality and transplant-related complications are usually high due to increased sensitivity to the alkylating agents and radiation commonly used for pre-transplant conditioning. Fludarabine monophosphate is a purine analogue that has been proven effective as a conditioning agent for chronic lymphocytic leukemia patients. We report a child with FA in leukemic transformation with thrombocytopenia and 20% myeloblasts who underwent successful BMT following conditioning with fludarabine/ATG/cyclophosphamide. The regimen was well tolerated, no transplant-related complications were observed, and engraftment was rapid. The child is currently 10 months post-BMT, in excellent clinical condition with a normal blood count, 100% chimerism and no sign of graft-versus-host disease (GVHD). We suggest that this fludarabine-based regimen may be effective in the conditioning of standard, as well as transforming, FA patients for BMT.

Stages in the development of radiation-induced thymic lymphomas in C57 BL/Ka mice: preleukemic cells become progressively resistant to the tumor preventing effects of a bone marrow graft

Fractionated whole body irradiation induces thymic lymphomas in C57 BL/Ka mice after 6-12 months. A graft of normal congenic bone marrow cells immediately after the last irradiation prevents the development of lymphomas by inducing the disappearance of preleukemic cells. When such a graft is performed one month later, it does not inhibit the emergence of tumors. It could be because, one month after irradiation, preleukemic cells become insensitive to the effects of the grafted bone marrow on their leukemogenic potential. To check this hypothesis, we have investigated the capacity of grafted bone marrow cells to prevent the development of lymphomas in mice inoculated with radiation-induced preleukemic cells collected at several time intervals after the completion of the radiation regimen. It was found that the bone marrow graft reduced the incidence of thymic lymphoma at day 2 (10 vs. 43%; p < 0.01) and 10 (39 vs. 86%; p < 0.01) but not at day 15 (64 vs. 80%; NS) or 30 (93 vs. 82%; NS). The inefficacy of the marrow graft was not associated with proliferation of the inoculate in the recipient thymus nor with inhibition by preleukemic cells of thymic repopulation by bone marrow precursors. The data provide evidence that preleukemic cells undergo intrinsic changes which are reflected by the acquisition of resistance to bone marrow grafts.

The preleukemic syndrome: clinical and laboratory features, natural course, and management

The clinical and laboratory features of the stages in the evolution of acute nonlymphocytic leukemia are reviewed. Based on a retrospective analysis of 34 patients who died with an acute myelomonoblastic leukemia, the "preleukemic syndrome" has been shown to display a clinical picture sufficiently specific to permit its recognition prospectively (i.e., before the development of overt leukemia). The results to date of a variety of prospective studies are reviewed, and the approach(es) to the management of these cases is considered.

Myelodysplastic (preleukemia) syndromes: the bone marrow factory failure problem

The myelodysplastic syndromes are a group of hematologic disorders that adversely affect the levels of hemoglobin, platelets, erythrocytes, and leukocytes. Although the cause of this syndrome is unknown, new diagnostic techniques have facilitated identification and classification of these diseases into five categories: refractory anemia (refractory cytopenia), refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, refractory anemia with excess blasts in transformation, and chronic myelomonocytic leukemia. Cytogenetic abnormalities may be present in more than 55% of the patients. Symptomatic patients should be assessed relative to life-threatening versus non-life-threatening cytopenias and age. Management consists of primarily supportive measures, although certain approaches that are currently being used or under investigation, such as concomitant administration of erythropoietin and other growth factors, show promise for the future.

Successful bone marrow transplant for Fanconi anaemia in transformation

We present a patient who was diagnosed as suffering from Fanconi anaemia at the age of 36 years. At the time of diagnosis his bone marrow showed features of pre-leukaemic transformation. He received an allogeneic bone marrow transplant (BMT) from his HLA-identical sibling. The post-transplant course was unremarkable with evidence of trilineage engraftment at day +32 and no acute or chronic GVHD. He is well with sustained engraftment and no haematological evidence of Fanconi anaemia 18 months post-transplant.

Busulfan, cyclophosphamide and melphalan as conditioning regimen for bone marrow transplantation in children with myelodysplastic syndromes

As typical disorders of the elderly, myelodysplastic syndromes (MDSs) are relatively unusual in childhood. Nevertheless, up to 17% of cases of pediatric acute myeloid leukemia may have a preleukemic phase. In young patients, the goal of treatment is eradication of the preleukemic malignant clone and reconstitution of normal hematopoiesis. Allogeneic bone marrow transplantation (BMT) has proved to be capable of this, but the optimal conditioning treatment to achieve eradication remains to be defined. Between May 1989 and June 1993, eight consecutive pediatric patients with MDS received a marrow transplant from an HLA-identical, mixed lymphocyte culture (MLC) non-reactive sibling. Diagnosis at time of presentation was refractory anemia with excess of blasts (RAEB) in two patients, RAEB in transformation (RAEB-t) in three, and juvenile chronic myelogenous leukemia (JCML, the pediatric counterpart of adult chronic myelomonocytic leukemia) in the remaining three children. Conditioning regimen consisted of busulfan, cyclophosphamide and melphalan, three alkylating agents potentially capable of killing also dormant preleukemic stem cells. The preparative regimen was very well tolerated, and all patients engrafted promptly. Six out of eight patients (75%) are alive and well with a median observation time of 20 months (range 8-34 months). Serial karyotype monitoring and molecular analyses have demonstrated a full chimerism of donor cells and the complete disappearance of trisomy 8 detected before transplant in three cases. All surviving patients have a Karnofsky score of 100%. One boy, affected by RAEB-t with monosomy 7 resistant to treatment with low-dose ara-C, relapsed 11 months after BMT, evolved in AML and died from progressive leukemia. Another patient with RAEB died on day +95 after BMT due to interstitial pneumonia of unclear etiology. This study confirms that allogeneic BMT is the treatment of choice in pediatric patients with MDS, and suggests that the employed conditioning regimen is a safe and effective means for eradicating the preleukemic malignant clone. Particularly noteworthy is that the three children with JCML obtained a complete remission and one of them is now a long-term survivor.

Human granulocyte colony-stimulating factor (G-CSF), the premier granulopoietin: biology, clinical utility, and receptor structure and function

In summary, both G-CSF and GM-CSF have been identified, cloned, and produced for pharmacologic use in humans. While both G-CSF and GM-CSF have had significant impact in the treatment of neutropenic states, G-CSF appears to be more advantageous than GM-CSF in overall efficacy and paucity of side effects. Much has been discovered about the structure of the G-CSF receptor but further work is necessary to determine its mechanism of signal transduction. As our understanding of G-CSF signaling advances, the therapeutic impact of our knowledge about G-CSF biology will evolve from the current focus on enhancing its effects in hematologic and oncologic illnesses to decreasing its effects in inflammatory conditions where overexhuberant neutrophil infiltration and activation cause disease.

Treatment of premalignancy: prevention of lymphoma in radiation leukemia virus-inoculated mice by cyclosporin A and immunotoxin

Radiation leukemia virus (RadLV)-induced preleukemic (PL) latency is characterized by the appearance of virus-infected PL cells in the thymus. The survival of these PL cells is dependent upon autostimulation with interleukin 4 (IL-4). We have intervened prophylactically in RadLV-induced preleukemia by using cyclosporin-A (CSA), which inhibits IL-4 production, and an immunotoxin (ITx) that kills PL cells. CSA efficiently inhibited IL-4 secretion from RadLV-induced PL and leukemic cells, and its administration to PL mice caused a significant delay in their death. An ITx consisting of anti-RadLV glycoprotein-70 (gp70) antibody coupled to ricin A chain efficiently inhibited protein synthesis in virus-infected cells in vitro and, when injected into PL mice, also delayed their death. Combined treatment with CSA and ITx prevented 75% of the treated PL mice from developing lymphoma. These results show that the development of malignancy from a premalignant state can be averted by a combination of therapeutic modalities that decrease the size and growth rate of the premalignant cell population.

Recent advances in biology and treatment of myelodysplasia

The myelodysplastic syndromes are clonal hematopoietic stem cell disorders characterized by varying degrees of pancytopenia and often a progression to acute myeloid leukemia. Recent evidence has linked myelodysplastic syndromes to environmental and occupational genotoxic exposure. Specific cytogenetic abnormalities are well described in myelodysplastic syndromes and have been demonstrated to be useful diagnostic and prognostic tools. Activation of protooncogenes such as ras and fms have also been noted in myelodysplastic syndromes; however, their contribution to the pathogenesis of the syndrome remains to be determined. Aggressive leukemia-like induction therapy, differentiating agents (low-dose cytarabine, 13-cis-retinoic acid) have had little impact on overall survival in myelodysplastic syndromes. The recombinant hematopoietic growth factors (granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor) may be of significant benefit to patients with myelodysplastic syndromes, although it remains to be determined whether they will have a substantial impact on survival. Allogeneic bone marrow transplantation is the only potentially curable treatment of myelodysplastic syndromes. The advanced age of these patients as well as the lack of histocompatible donors restricts this modality to only a small proportion of patients.

Properties of tumor infiltrated cells induced by N-CWS

Analysis of surface marker of cells after intratumor injection with Nocardia rubra cell wall skeleton (N-CWS) resulted in gradually increasing percentage of macrophage, Pan T and BoCD4+ cells. Proportion of BoCD8+ cells gradually increased from 4th day and then decreased from 8th day after the injection. Fresh tumor infiltrated cells obtained from lymphatic nodule at 8 days after injection of N-CWS showed cytotoxic activity against bovine leukemia cell line, but this activity decreased with the time of cultivation and no activity could be detected after 14 days cultivation. These cultured cells were injected twice to lymphatic nodule at one week interval for adoptive immunotherapy and found to induce complete regression of nodule after 5 weeks from first injection.

Chemotherapy and immunotherapy of bovine leukosis

To prevent the progression of the disease, we treated leukemic or preleukemic cows with (1) adriamycin (ADM) entrapped in liposomes conjugated with monoclonal antibody, c143, against tumor-associated antigens (TAA) of bovine leukemic cells and (2) an immunotherapy using an immunopotentiator consisting of the cell wall skeleton of Nocardia rubra (N-CWS). Five leukemic or preleukemic cows with TAA-positive peripheral blood lymphocytes (PBL) received four injections of ADM alone (0.4 mg/kg body weight) or c143-conjugated liposomes containing the same dose of ADM (L-ADM-c143) through the jugular vein at about 4-day intervals. In three animals treated with L-ADM-c143, the TAA-positive cells gradually decreased with treatment and finally two animals became TAA-negative during a 6-week period and a 14-week period after treatment, respectively. About 6 weeks later, however, TAA-positive cells gradually increased. In the control, two animals treated with ADM alone showed no decrease of TAA-positive cells. Five TAA-positive animals with enlarged subcutaneous lymphatic nodules, each nodule estimated to be from 1 to 4 cm3 in size, were treated by injection of N-CWS into the tumors. Complete regression of tumor was observed in seven out of ten tumors treated in five animals. Decrease of TAA-positive cells was also observed in PBL for all five treated animals. In one animal, the TAA-positive cells remained low for at least 280 days after treatment. This study documents that ADM treatment and intralesionally administered N-CWS are effective in the treatment of bovine leukosis.

Preleukaemia and myelodysplastic syndromes today

The clinical picture of myelodysplastic syndromes (MDS) results from the expansion of an abnormal clone of haemopoietic stem cells that has undergone premalignant transformation. Different types of "oncogene" may be involved in this process, some of which code for growth factors and their receptors, some for membrane or cytoplasmic proteins and some for nuclear binding proteins. The insults causing gene mutations are not known, though chemical, viral or radiation damage could be important. The most striking feature of MDS is the inadequate production of dysplastic, poorly functional cells as a result of impaired differentiation and premature cell death in the bone marrow. Treatment is currently directed to supportive therapy with blood components and antibiotics, attempts to stimulate proliferation and differentiation with recombinant human growth factors, and, in a few cases, bone marrow transplantation. Chemotherapy alone has met with little success.

The preleukemic syndrome (hematopoietic dysplasia)

It has been recognized for many decades that epithelial dysplasia can represent an early histological sign of epithelial neoplasia. So it is with hematopoietic tissue wherein dysplasia of bone marrow cells can be an early sign of impending acute myeloid leukemia. Although this 'preleukemic syndrome' of hematopoietic dysplasia can often be identified well in advance of the classic histological signs of acute leukemia, a wide variety of basic studies on bone marrow cells, from patients and from experimental animals with induced preleukemia, clearly indicate that the preleukemic marrow cells are members of a fully established neoplastic clone. Consequently, it is likely that the preleukemic syndrome is merely acute leukemia diagnosed earlier than usual and which, in some patients, can be very slowly progressive, and in others may not progress at all. This article reviews the evidence in support of the notion that the preleukemic syndrome is an 'early leukemia', places the preleukemic syndrome in the context of a larger group of myelodysplastic disorders, reviews the laboratory studies of value for both diagnosis and for use in the assessment of prognosis, and summarizes the therapeutic options available for the management of patients with this disorder.

[Induction of myelogenous differentiation: a therapeutic possibility for preleukemia and acute leukemia?]

Human acute myelogenous leukemia often arises from a transformation at the stem cell level leading to a block in differentiation. The malignant cell, therefore, remains in the proliferative pool and rapidly accumulates. In preleukemia, also known as myelodysplastic syndromes, the malignant clone is already established, leading to disturbed hematopoiesis. One therapeutic approach, therefore, might be to overcome this block in differentiation and thus shift the cell from the proliferative into the differentiating pool. For several years now research in leukemia has focused on study of the proliferation and differentiation of normal and leukemic hematopoietic cells. Numerous substances have been identified which are able to trigger differentiation in myeloid cells, including the retinoids, vitamin D, tumor necrosis factor and hematopoietic hormones. The possible role of these agents in the treatment of preleukemia and acute myelogenous leukemias is discussed.

[Chemotherapeutic effects in hypoplastic leukemia]

Clinical effects of a low dose of behenoyl ara-C (LD-BHAC) and K-18, an IgG-melphalan conjugate, were studied in hypoplastic leukemia (HL). Among 8 cases of HL treated with LD-BHAC regimen, in which 50 mg BHAC was administered daily by one-hour drip infusion for 14 days, 4 achieved complete remission (CR) and 2, partial remission (PR). The response rate (CR + PR) was 75%. Hematological toxicities were observed in most of the cases. The peak level of serum ara-C concentration, 3.62-18.9 ng/ml (mean: 11.74 ng/ml), was observed at cessation of infusion, and an ara-C level of 2.75-48.9 ng/ml (mean: 3.45 ng/ml) was still present in the blood 6 hours after cessation of infusion. Six cases of HL were treated with K-18. Eight tablets of K-18, containing 30 mg per tablet, were given daily. Two of 6 cases achieved CR with little hematological toxicities. LD-BHAC and K-18 can be expected in the treatment of hypoplastic leukemia and its related diseases such as hypoplastic preleukemia in the aged.

[Clinical investigation of interferons in the preleukemic state (CML and MDS)]

We treated 11 patients who had Philadelphia-chromosome-positive chronic myelogenous leukemia with natural interferon alpha (human lymphoblastoid interferon; HLBI). HLBI was given at 6-12 X 10(6) u/day i.m. or i.s.c. during induction therapy. Nine patients responded to the treatment, of whom 7 had hematologic remission and 2 had partial remission. Six patients with MDS or hypoplastic leukemia, and 3 patients with overt leukemia from MDS were treated with recombinant interferon gamma (GI-3). GI-3 was given at 0.4 X 10(6) u/m2 of body-surface area per day i.s.c. or i.v. for 4-6 weeks. In 2 patients with RAEB and hypoplastic leukemia, the blast cell count in bone marrow decreased from 8-16% to 2-3% after 4 weeks of administration. In another patient with hypoplastic leukemia, blast cells in the marrow did not decrease, but anemia was improved without transfusion, increasing the bone marrow NCC and erythroblast count. In patients with overt leukemia and CMML, no clinical effect was obtained. Interferons can therefore be offered to patients in a preleukemic state.

Treatment of preleukemic syndromes with marrow transplantation

Thirty patients with advanced preleukemic syndromes were treated with marrow transplantation. Most cases were diagnosed by the presence of peripheral pancytopenia and a diagnostic marrow examination but in 6 of the 30 patients pretransplant chromosome studies were instrumental in establishing the diagnosis. Three patients prepared for transplantation with cyclophosphamide alone recurred with their disease within 6 months of transplantation. The other 27 patients were treated with cyclophosphamide and total body irradiation. Twenty of these 27 patients had preleukemia not associated with prior therapy or severe marrow fibrosis. Thirteen of these 20 are alive and well 9 to 56 months from transplant and 7 died, 4 of interstitial pneumonia, 2 of candida septicemia, and 1 of disseminated zoster. There have been no disease recurrences in this group. The remaining preleukemic patients, which include 3 patients transplanted for preleukemia secondary to prior therapy and 4 patients transplanted for preleukemia associated with severe marrow fibrosis, have all died. Major problems in these patients included disease recurrence (2 cases) and, in those with severe marrow fibrosis, graft failure (2 cases). These results suggest that for patients with life-threatening pancytopenia due to spontaneous preleukemia without severe marrow fibrosis, marrow transplantation can prolong disease-free survival and may result in cure of the disease.

The treatment of myelodysplastic syndromes

The available data fail to support a standard therapy for MDS. Any therapy should therefore, include participation in a well designed clinical trial. The MDS include patients with a variety of prognoses. Since most studies show that death from infection and bleeding are more likely than progression to frank leukaemia, attention to supportive care is crucial for all patients with MDS. Some patients with MDS may be successfully supported with transfusions and observation for prolonged periods. Patients with significant comorbid disease or patients without increased marrow myeloblasts are good candidates for this conservative approach. Conversely, young patients have a better likelihood of benefit from aggressive therapy, and intensive chemotherapy or allogenic bone marrow transplantation should be considered. Patients with preleukaemia related to prior cytotoxic therapy are another poor prognosis group for whom aggressive therapy may be the best alternative. Therapy with low-dose ara-C or other differentiating agents should be considered investigational and unproven until comparative trials can demonstrate a definitive survival advantage. In addition to comparative trials, innovative clinical studies are needed to address differentiation as an in vivo mechanism of action and its importance in MDS therapy.

Marrow transplantation in preleukemia

Preleukemia has generally been treated by palliative measures. Several reports have indicated that cytarabine given as low-dose infusion results in responses, albeit short lived, in a fraction of patients. We have shown recently that marrow transplantation offers a useful alternative. Twelve patients have been treated and followed for a minimum of 1 year. Three were conditioned with cyclophosphamide (CY) only, and all died with recurrent or persistent disease. Nine were conditioned with CY and total-body irradiation; all but 1 had lasting engraftment, and 7 are surviving, free of disease, 16-36 (median 27) months after transplantation. These data show that marrow transplantation can provide successful therapy for preleukemia.

Granulocytic sarcoma. A new finding in the setting of preleukemia

Preleukemia is a well-defined syndrome of hematopoietic dysfunction that may antedate the development of acute myelogenous leukemia. Granulocytic sarcoma refers to neoplastic infiltration in the skin, composed of immature cells of the granulocyte series. We report two cases of granulocytic sarcoma in the setting of preleukemia. The clinical importance of these cases, as well as the cutaneous manifestations of leukemia and the clinical spectrum of granulocytic sarcoma, are presented.

Allogeneic marrow transplantation in the treatment of preleukemia

Ten patients with preleukemia and life-threatening pancytopenia were treated with marrow transplantation. In all ten cases allogeneic marrow was successfully engrafted. In three patients prepared for transplantation with cyclophosphamide alone, the abnormal cell clone either persisted or reemerged within 6 months of transplantation. The other seven patients were treated with cyclophosphamide plus total body irradiation before transplantation and six of the seven are alive and well without evidence of disease from 7 to 25 months after transplantation. These results suggest that cyclophosphamide alone before marrow transplantation is incapable of eradicating the abnormal clone. Cyclophosphamide combined with total body irradiation appears more effective, although more time is needed for full evaluation of results. This experience also emphasizes the importance of performing chromosome studies before transplantation for pancytopenic states in order to identify cases of preleukemia.

Treatment of therapy-induced preleukemic syndrome

Two young adult patients with therapy-induced preleukemic syndrome and Hodgkin's disease as primary malignancy were treated with aggressive antileukemic regimens before the establishment of leukemic conversion. Pretreatment clinical staging procedures did not reveal recurrence of Hodgkin's disease. One of the regimens consisted of an HLA-identical allogeneic bone marrow transplant and the other of high dose cytosine arabinoside. Both therapeutic approaches have proved successful in restoring normal hematopoiesis with reversal to normal karyotypes and unmaintained remissions 556 and 192 days post-treatment. The rationale for such a therapeutic approach in the preleukemic stage of therapy-induced leukemogenesis is discussed.

[Dysmyelopoietic syndrome 7 years after melphalan treatment of multiple myeloma. Clinical case]

A case of myelodysplasia (refractory anaemia with excessive blasts) arising 7 years after a 3 year period of intermittent monthly treatment cycles with melphalan for multiple myelomas is reported. This is another example of preleukaemic syndrome possibly caused by melphalan. Among the possible pathogenetic mechanisms, the incidence of cyclic episodes of medullary hypoplasia are emphasised.

Restoration of normal hematopoiesis by bone marrow ablation and allogeneic marrow transplantation in a case of Hodgkin's disease therapy-related preleukemia

Therapy-related leukemias are generally preceded by a preleukemic phase of several months duration, characterized by pancytopenia, abnormal bone marrow findings, and nonrandom chromosomal abnormalities in almost all cases. No specific therapeutic guidelines are recommended in this preleukemic phase or any other type of preleukemia; aggressive combination chemotherapy is usually withheld until the full expression of leukemia. A 22-yr-old man with therapy-related preleukemia following treatment of Hodgkin's disease received as primary treatment ablative chemotherapy followed by marrow transplantation from his histocompatible sister. At day 316, the patient is still in complete bone marrow recovery with a normal donor karyotype. In the light of the very poor results obtained with conventional chemotherapy regimens once the leukemic phase is established, we suggest that bone marrow transplantation, if undertaken before leukemic conversion, may be the treatment of choice in young adults with therapy-related preleukemia.

The preleukemic syndrome

While the preleukemic syndrome (PLS) is not a homogeneous entity, its spectrum of clinical and laboratory findings has been sufficiently characterized to allow increasing certainty in its recognition. Approximately 25 percent of these patients can be expected to develop overt acute nonlymphocytic leukemia (ANLL) within an average of two to three years, and another 40 percent will die of non-leukemic complications usually related to their cytopenias within a similar time period. The remaining patients may be stable and survive for prolonged periods. Accumulating evidence indicates that in the PLS, a stem cell neoplastic clonal proliferation has already been established and may frequently be demonstrated by cytogenic analysis or culture of marrow hematopoietic cells.