LEUKEMIA IN PATIENTS WITH BREAST-CANCER FOLLOWING ADJUVANT CHEMOTHERAPY AND OR POSTOPERATIVE RADIATION-THERAPY/

We investigated the possible etiological role of adjuvant chemotherapy and postoperative radiation therapy in the development of leukemia. A case-control design with four controls matched to each case of leukem ia from a cohort of women who had been treated for breast cancer durin g the years from 1970 to 1985 was used. Thirteen (0.23%) of the women in this cohort developed leukemia over varying lengths of follow-up ti me, ranging from 3 to 14 years. A higher percentage of the leukemia ca ses previously had adjuvant chemotherapy compared to their matched con trols (54% versus 13%) The relative odds estimate of developing leukem ia after chemotherapy compared to no chemotherapy was 14.8 (95% C.I. ( 1.8; 125.3) p < 0.01). This estimate and the test of statistical signi ficance was based on the likelihood function for matched sets with one case and more than one control. Approximately the same percentage of leukemia cases as their controls had received postoperative regional r adiation therapy (28% versus 23%). No significant association was foun d between postoperative radiation therapy and development of leukemia. A combination of adjuvant chemotherapy and postoperative radiation th erapy was found more frequently in the leukemia cases than in their ma tched controls (33% versus 9%). The leukemia developing in patients ha ving received adjuvant chemotherapy was frequently therapy resistant, resulting in a short survival.