Preleukemia: the normal side of cancer.

PURPOSE OF REVIEW: In the present review, we will define the preleukemic state. We aim at increasing awareness and research in the field of preleukemia that will nurture targeted therapy for the earlier steps of leukemia evolution. RECENT FINDINGS: Emerging evidence supports the role of hematopoietic stem/progenitor cells carrying recurrent leukemia-related mutations as the cell of origin of both myeloid and lymphoid malignancies. The preleukemic stem cells can maintain at least to some extent their functionality; however, they have increased fitness endowed by the preleukemic mutations that lead to clonal expansion. SUMMARY: The latent preleukemic period before overt leukemia presents can take years, and the majority of carriers will never develop leukemia in their lifetime. The preleukemic state is not rare, with greater than 1% of individuals having acquired one or more of the recognized preleukemic lesions. The high frequency of such abnormalities in the population may be the cost of growing old; however, another view could be that in order to survive to old age, the hematopoietic system must adapt to create robust hematopoietic stem/progenitor cells with an increased fitness and clonal expansion. Hence, leukemia does not necessarily start as a disease, but rather as a need, with the normally functioning preleukemic hematopoietic stem cells trying to maintain health for years but in time succumbing to their own acquired virtues.

Clonal selection in xenografted TAM recapitulates the evolutionary process of myeloid leukemia in Down syndrome.

Transient abnormal myelopoiesis (TAM) is a clonal preleukemic disorder that progresses to myeloid leukemia of Down syndrome (ML-DS) through the accumulation of genetic alterations. To investigate the mechanism of leukemogenesis in this disorder, a xenograft model of TAM was established using NOD/Shi-scid, interleukin (IL)-2Rγ(null) mice. Serial engraftment after transplantation of cells from a TAM patient who developed ML-DS a year later demonstrated their self-renewal capacity. A GATA1 mutation and no copy number alterations (CNAs) were detected in the primary patient sample by conventional genomic sequencing and CNA profiling. However, in serial transplantations, engrafted TAM-derived cells showed the emergence of divergent subclones with another GATA1 mutation and various CNAs, including a 16q deletion and 1q gain, which are clinically associated with ML-DS. Detailed genomic analysis identified minor subclones with a 16q deletion or this distinct GATA1 mutation in the primary patient sample. These results suggest that genetically heterogeneous subclones with varying leukemia-initiating potential already exist in the neonatal TAM phase, and ML-DS may develop from a pool of such minor clones through clonal selection. Our xenograft model of TAM may provide unique insight into the evolutionary process of leukemia.

Anti-CD117 immunotherapy to eliminate hematopoietic and leukemia stem cells.

Precise replacement of diseased or dysfunctional organs is the goal of regenerative medicine and has appeared to be a distant goal for a long time. In the field of hematopoietic stem cell transplantation, this goal is now becoming tangible as gene-editing technologies and novel conditioning agents are entering the clinical arena. Targeted immunologic depletion of hematopoietic stem cells (HSCs), which are at the very root of the hematopoietic system, will enable more selective and potentially more effective hematopoietic stem cell transplantation in patients with hematological diseases. In contrast to current conditioning regimes based on ionizing radiation and chemotherapy, immunologic conditioning will spare mature hematopoietic cells and cause substantially less inflammation and unspecific collateral damage to other organs. Biological agents that target the stem cell antigen CD117 are the frontrunners for this purpose and have exhibited preclinical activity in depletion of healthy HSCs. The value of anti-CD117 antibodies as conditioning agents is currently being evaluated in early clinical trials. Whereas mild, antibody-based immunologic conditioning concepts might be appropriate for benign hematological disorders in which incomplete replacement of diseased cells is sufficient, higher efficacy will be required for treatment and elimination of hematologic stem cell malignancies such as acute myeloid leukemia and myelodysplastic syndrome. Antibody-drug conjugates, bispecific T-cell engaging and activating antibodies (TEAs), or chimeric antigen receptor (CAR) T cells might offer increased efficacy compared with naked antibodies and yet higher tolerability and safety compared with current genotoxic conditioning approaches. Here, we summarize the current state regarding immunologic conditioning concepts for the treatment of HSC disorders and outline potential future developments.

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.

Preleukemia: one name, many meanings.

Definition of preleukemia has evolved. It was first used to describe the myelodysplastic syndrome (MDS) with a propensity to progress to acute myeloid leukemia (AML). Individuals with germline mutations of either RUNX1, CEBPA, or GATA2 can also be called as preleukemic because they have a markedly increased incidence of evolution into AML. Also, alkylating chemotherapy or radiation can cause MDS/preleukemia, which nearly always progress to AML. More recently, investigators noted that AML patients who achieved complete morphological remission after chemotherapy often have clonal hematopoiesis predominantly marked by either DNMT3A, TET2 or IDH1/2 mutations, which were also present at diagnosis of AML. This preleukemic clone represents involvement of an early hematopoietic stem cells, which is resistant to standard therapy. The same clonal hematopoietic mutations have been identified in older 'normal' individuals who have a modest increased risk of developing frank AML. These individuals have occasionally been said, probably inappropriately, to have a preleukemia clone. Our evolving understanding of the term preleukemia has occurred by advancing technology including studies of X chromosome inactivation, cytogenetics and more recently deep nucleotide sequencing.

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.

Leukemia: stem cells, preleukemia and cure.

Several new or evolving concepts of leukemia biology and treatment are considered including: most leukèmias result from transformation of a stem cell, their phenotype reflecting the site of clonal expansion rather than transformation; most leukemias are preceded by one or more preleukemia phases; and cure may be possible by re-establishing preleukemia or forcing maturation of leukemia cells.

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.

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.

Down syndrome preleukemia and leukemia.

Children with Down syndrome (DS) and acute leukemias acute have unique biological, cytogenetic, and intrinsic factors that affect their treatment and outcome. Myeloid leukemia of Down syndrome (ML-DS) is associated with high event-free survival (EFS) rates and frequently preceded by a preleukemia condition, the transient abnormal hematopoiesis (TAM) present at birth. For acute lymphoblastic leukemia (ALL), their EFS and overall survival are poorer than non-DS ALL, it is important to enroll them on therapeutic trials, including relapse trials; investigate new agents that could potentially improve their leukemia-free survival; and strive to maximize the supportive care these patients need.

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.

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.

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.

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.

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.

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.

Diagnosis and treatment of the preleukemic syndrome (hemopoietic dysplasia).

Retrospective and prospective observations have established the existence of a recognizable hematologic syndrome preceding the development of acute nonlymphocytic leukemia. This syndrome, which has been termed the "preleukemic syndrome" or "hemopoietic dysplasia", appears to be a stage in a multiphasic myeloproliferative disorder, rather than a separable disease with a propensity to develop leukemia. All products of the marrow stem cell are involved. The panmyelopathy begins as a red cell disease (eg, a refractory or sideroblastic anemia) and progresses to involve megakaryocytes and platelets and finally granulocytes or monocytes, or both; the terminal event is acute nonlymphocytic (myelomonoblastic) leukemia. Prospective documentation is needed in order to define the natural course of this marrow disease. Such studies are now in progress and should provide important information concerning the pathophysiology of acute nonlymphocytic leukemia.

[Dysmyelopoietic syndrome 7 years after melphalan treatment of multiple myeloma. Clinical case]. / Sindrome dismielopoietica sette anni dopo trattamento di mieloma multiplo con melphalan. Caso clinico.

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.