Incidence, previous treatment and chromosome characteristics of secondary acute non-lymphocytic leukemia

Therapy-related leukemia associated with alkylating agents

The leukemogenic potential of alkylating agents has been known for many years and almost all alkylating agents in clinical use have been shown to increase the risk of leukemia. With these drugs the risk of leukemia appears to increase with increasing patient age, as does the risk of de novo myeloid leukemia in the population. Susceptibility to alkylating agent-associated leukemia is influenced by the genetic constitution of the patient, and by the nature of the exposure. To illustrate the importance of these factors in etiology of leukemia, this paper discusses the contribution of disorders such as Fanconi anemia and neurofibromatosis to susceptibility to alkylating agent-associated leukemia. This paper also discusses the contribution of alkylating agents and other therapeutic exposures in the etiology of leukemias occurring after autologous bone marrow transplant.

Therapy related leukemias: susceptibility, prevention and treatment

Acute leukemia is the most frequent therapy-related malignancy. Together with the increasing use of chemo- and radiotherapy, individual predisposing factors play a key role. Most of secondary leukemias can be divided in two well-defined groups: those secondary to the use of alkylating agents and those associated to topoisomerase inhibitors. Leukemias induced by alkylating agents usually follow a long period of latency from the primary tumour and present as myelodysplasia with unbalanced chromosomal aberrations. These frequently include deletions of chromosome 13 and loss of the entire or of part of chomosomes 5 or 7. The loss of the coding regions for tumor suppressor genes from hematopoietic progenitor cells is a particularly unfavourable event, since the remaining allele becomes susceptible to inactivating mutations leading to the leukemic transformation. The tumorigenic action of topoisomerase inhibitors is on the other hand due to the formation of multiple DNA strand breaks, resolved by chromosomal translocations. Among these, chromosome 11, band q23, where the myeloid-lymphoid leukemia (MLL) gene is located, is often involved. Frequent partners are chromosomes 9, 19 and 4 in the t(9;11), t(19;11) and t(4;11) translocations. Younger age, a mean period of latency of 2 years and monocytic subtypes are characteristic features of this type of leukemia. Among patients at risk for secondary leukemia, those with Hodgkin's disease are the most extensively studied, with the major impact of alkylating agents included in the chemotherapy schedule. The same is true for non-Hodgkin's lymphoma, while in multiple myeloma and acute lymphoblastic leukemia determinants are the dose of melphalan and of epypodophyllotoxin, respectively. Patients with breast, ovarian and testicular neoplasms are also at risk, in particular if trated with the association of alkylating agents and topoisomerase II inhibitors. According to the EBMT registry, in patients with lymphoma treated with high-dose therapy and autologous stem cell transplantation the cumulative risk of inducing leukemia at 5 years is 2.6%. Among treatment options, supportive therapy is indicated in older patients, while allogeneic stem cell transplantation, related or matched-unrelated, is feasible in younger patients. These data indicate the need for the identification of predisposing factors for secondary leukemia. In particular, frequent follow-up of patients at high-risk should be performed and any peripheral blood cytopenia should be considered suspicious. Whenever possible, the exclusion of drugs known to be leukemogenic from the treatment schedules should be considered, especially in young patients.

Acute leukaemia after hydroxyurea therapy in polycythaemia vera and allied disorders: prospective study of efficacy and leukaemogenicity with therapeutic implications

Fifty consecutive patients, 30 of whom had polycythaemia vera (PV), 10 essential thrombocythaemia (ET), and 10 myelofibrosis (MF), entered a long-term prospective study of hydroxyurea (HU) therapy. The indication for treatment was mainly thrombocytosis or symptomatic splenomegaly. Control of erythrocytosis and thrombocytosis was achieved in 70% of the patients. Continuous maintenance treatment was required. In 15% of responding patients with thrombocytosis, unexpected rises of the platelet count occurred during maintenance therapy. Severe thrombo-embolic events occurred in 6 patients. The size of the spleen decreased in all patients who did not develop thrombocytopenia and could absorb adequate HU doses. Acute leukaemia (AL) was diagnosed in 9 patients and a myelodysplastic syndrome in one. Seven of them had been treated with HU alone. Among the patients with PV and ET, 6 developed AL and 4 of them were treated with HU alone (3 PV and 1 ET), giving an incidence of 10.5%. In previously untreated patients with initially normal karyotypes (n = 19), chromosome abnormalities developed during HU therapy in 7 (37%). Our results indicate that HU should be regarded as leukaemogenic, at least when used for treatment of PV and allied diseases. Since myelosuppressive treatment of PV does not prolong survival, the use of HU should be restricted to patients in whom the treatment indication outweights the risk of leukaemia induction.

Specific chromosomal mutagenesis observed in stimulated lymphocytes from patients with S-ANLL

An analysis of R-banded PHA-stimulated lymphocytes from 13 patients with secondary acute non-lymphocytic leukemia (S-ANLL) following breast cancer or lymphoma, and treatment by alkylating agents and/or radiotherapy, is reported. We found that chromosomes 5, 7, 11 and 17 are over-involved in structural rearrangements. These anomalies are similar to those observed in the same categories of patients without S-ANLL, and after in vitro treatment of normal lymphocytes by the alkylating agent melphalan. These anomalies are thus likely to be induced by treatment, independently of S-ANLL. However, the same chromosomes (5, 7, 11 and 17) are recurrently deficient in leukemic S-ANLL clones. In spite of these similarities, it remains unlikely that the deficiencies observed in leukemic clones were directly induced at the time of treatment. Probably, treatment of primary cancers induces nonrandom mutations of recessive genes located on these chromosomes as also indicated by chromosomal lesions. Various rearrangements including deletions of the homologous normal counterparts may then occur, unmasking mutated recessive genes. The latter stage would be concomitant with the leukemogenic process.

Cytogenetic abnormalities in acute leukemia complicating melphalan-treated multiple myeloma

The cytogenetic findings in 11 patients with multiple myeloma in whom a myelodysplastic syndrome or an acute nonlymphocytic leukemia developed are reported. All patients were treated with oral melphalan for 2-9 years in a total dose of 0.5-4.1 g. When examined during the myelodysplastic or leukemic phase, all patients had an abnormal bone marrow karyotype, hypodiploid in nine of the 11 cases. The chromosome abnormalities were clearly nonrandom and comprised a 5q deletion in three cases, monosomy 5 in four cases, deletion 7q--in two cases, and monosomy 7 in three cases. Loss of material from the long arm of chromosomes 5, 7, or both was found in eight patients. The different chromosome abnormalities were not associated with any specific morphological or clinical features.

The chemotherapeutic drug melphalan induces breakage of chromosomes regions rearranged in secondary leukemia

A cytogenetic study is reported on the lesions induced in vitro by melphalan, a currently used anticancer drug. The distribution of 2166 breakpoints shows that they do not occur at random. There is a large excess of breaks in region q1 of chromosome 9 and R bands are significantly more affected than G-band-rich segments. Furthermore, some regions of chromosomes 5, 7, 11, and 17, which are the chromosomes usually rearranged and deleted in secondary leukemias, presumably induced by such treatments, are frequently affected. It is presumed that the frequent involvement of 9q1 largely reflects preexisting monostrand breaks. The frequent breakage of chromosomes 5, 7, 11, and 17 and of R bands in general, which are known to be G-C rich, may result from the preferential methylation of the O6 of guanine by melphalan.

Secondary leukemia with a translocation (8;21)?

The clinical features and cytogenetic changes of acute myeloid leukemia (AML) developing 10 years after radiotherapy and chemotherapy (for osteosarcoma) are described. Features of both de novo AML [FAB M2 morphology, t(8;21), and "secondary leukemia" (additional cytogenetic changes, resistance to chemotherapy) were present. The importance of differentiation between primary and "therapy-linked" disease, and the difficulties in making such a distinction, are discussed.

The iatrogenic leukaemias induced by radio- and/or chemotherapy

A short review, limited to recently published series of data, has been compiled on the 'therapy-induced' secondary malignancies. Their frequency, peak of incidence, haematological and clinical criteria, the influence of age, treated primary disease, choice of drug(s) and modality of prescription and the role of genetic and environmental factors are analyzed. The risk varies between 0.6 and 20.5% after different treatment forms. Some suggestions for the choice of treatment of chronic malignant disorders, and for the design of future epidemiological studies are given.

Cytogenetic analyses in 89 patients with secondary hematologic disorders--results of a cooperative study

Eighty-nine patients who developed a secondary hematologic disorder and were studied with chromosome analysis were collected from nine institutions. The results of the study confirmed previous findings, in particular, -5/5q-, -7/7q-, -17, and +21 were the most frequently encountered aberrations. Moreover, a t(1;7)(p11;p11) was reported in four cases and consistent chromosome abnormalities were observed in a small group of patients who had been treated only with surgery, but not with chemo- or radiotherapy for a previous tumor.

Development of acute nonlymphocytic leukaemia (ANLL) in myelomatosis

On the basis of the literature, so-called secondary acute nonlymphocytic leukaemia (S-ANLL) in myelomatosis is reviewed. Using the banding technique, cytogenetic changes including hypodiploidy and partially or totally missing chromosomes # 5 and # 7 are recorded. The findings are in accordance with the cytogenetic changes seen in S-ANLL in other malignancies which have been treated with cytostatics, especially alkylating agents. So, S-ANLL in myelomatosis seems to be a result of treatment with cytostatics, though a causal relationship has to be documented.