Purpose: Adjuvant chemotherapy for breast cancer has been the routine practice in the past decade. A number of studies have observed an increased incidence of treatment-related leukemias following chemotherapy with alkylating agents and/or topoisomerase II inhibitors. We evaluated the incidence of treatment-related leukemias in breast cancer patients treated in four adjuvant and two neoadjuvant chemotherapy trials at The University of Texas M.D. Anderson Cancer Center.
Patients and methods: Between 1974 and 1989, 1,474 patients with stage II or III breast cancer were treated in six prospective trials of adjuvant (n = 4) or neoadjuvant (n = 2) chemotherapy with fluorouracil, doxorubicin, and cyclophosphamide (CTX) (FAC) with or without other drugs. The median observation time was 97 months. In 1,107 patients, FAC chemotherapy was given postoperatively; 367 patients received induction chemotherapy, as well as postoperative chemotherapy. Eight hundred ten patients had surgery followed by radiotherapy and chemotherapy; 664 patients had surgery and chemotherapy only. Patients in two adjuvant and one neoadjuvant study received higher cumulative doses of CTX compared with those in the other studies.
Results: Fourteen cases of leukemia were observed. Twelve of these patients had received radiotherapy and chemotherapy, and two had received chemotherapy only. Six of the reported patients with leukemia were treated with a cumulative CTX dose of greater than 6 g/ m2. Five of these patients had received both radiotherapy and chemotherapy. The median latency period in the 14 patients was 66 months (range, 22 to 113). Six of 10 patients with adequate cytogenetic analyses had abnormalities that involved chromosomes 5 and/or 7. The rest of the patients had nonspecific cytogenetic abnormalities or lacked cytogenetic information. The 10-year estimated leukemia rate was 1.5% (95% confidence interval [CI], 0.7% to 2.9%) for all patients treated, 2.5% (95% CI, 1.0% to 5.1%) for the radiotherapy-plus-chemotherapy group, and 0.5% (95% CI, 0.1% to 2.4%) for the chemotherapy-only group; this difference was statistically significant (P = .01). The 10-year estimated leukemia risk for the higher-dose (> 6 g/m2) CTX group was 2% (95% CI, 0.5% to 5.0%) compared with 1.3% (95% CI, 0.4% to 3.0%) for the lower-dose group, a difference that was not statistically significant (P = .53).
Conclusion: These data illustrate that patients treated with adjuvant FAC chemotherapy plus radiotherapy have a slightly increased risk of leukemia. This information needs to be considered in the treatment plans for patients with breast cancer. However, for most patients, the benefits of adjuvant therapy exceed the risk of treatment-related leukemia.