Purpose: Since large numbers of patients with early-stage breast cancer now receive adjuvant chemotherapy containing cyclophosphamide, a known leukemogenic agent, it is important to determine the risk of secondary acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Therefore, we identified all cases of AML or MDS developing in patients treated on six clinical adjuvant chemotherapy trials conducted by the Eastern Cooperative Oncology Group (ECOG).
Patients and methods: The patients population included 2,638 patients with previously untreated primary operable breast cancer entered onto six clinical trials conducted by the ECOG between 1978 and 1987. There are 19,200 persons-years of follow-up study and a mean follow-up duration of 7.3 years. Clinical data were obtained from flow sheets submitted to the ECOG Data Management Office.
Results: Of 2,638 patients at risk with 19,200 person-years of follow-up study, three patients developed MDS (two with a characteristic cytogenetic abnormality). Two patients developed acute leukemia; however, one had adult T-cell leukemia associated with human T-lymphotrophic virus type 1 (HTLV-1) and a second patient developed AML after receiving additional cyclophosphamide for metastatic breast cancer. The estimated incidence rate for MDS is three per 19,200 or 16 per 100,000 person-years of follow-up study with a 95 percent confidence interval of three to 46 per 100,000 person-years. If all five patients (three MDS and two acute leukemia) are included, the estimated incidence rate is five per 19,200 or 26 per 100,000 person-years of follow-up study with a 95 percent confidence interval of eight to 61 per 100,000 person-years.
Conclusion: These data suggest that the risk of secondary AML or MDS among patients with early breast cancer who receive standard-dose cyclophosphamide-containing adjuvant chemotherapy is not much higher than in the general population. However, physicians must remain alert to the possible long-term consequences of alkylating agent and anthracycline-based chemotherapy.