Impact of a reduced dose intensity of adjuvant anthracycline based chemotherapy in a population-based cohort of stage I-II breast cancers

Background: Reductions in the dose intensity (DI) of adjuvant anthracycline-based chemotherapy in early stage breast cancer are frequently required due to treatment toxicity or poor tolerance, but the implications of a minimal reduction in DI on clinical outcome remain uncertain. Patients and methods: Women with stage I-II breast cancer treated with adjuvant adriamycin and cyclophosphamide (AC) from 199095 were identified in a provincial breast cancer database. Cases were classified into four cohorts: (1) all cycles delivered at full dose and on time; (2) one single dose reduction or dose delay; (3) > 1 dose reduction or dose delay; (4) <2 cycles of chemotherapy delivered. Results: 484 eligible cases were identified (cohort (1): n = 268; (2): n=88; (3): n=89; (4) n=39). Slight imbalances in lymph node status (p=0.05) and adjuvant hormonal therapy (p=0.05) were observed between the cohorts. Fifty-five per cent (267/484) of the patients had node-positive disease and 33% (158/484) were ER+. 45% of cases had a reduction in DI. With a median follow-up of 9.6 years, there were no significant differences in relapse-free survival (p=0.94), breast cancer-specific survival (p=0.87) or overall survival (p=0.86) between the four cohorts. Outcomes were independent of hormone receptor status. Conclusions: Although toxicity related reductions in the DI of adjuvant AC chemotherapy for early stage breast cancer are common, they did not appear to significantly impact on clinical outcomes in this population-based cohort of women with stage I-II breast cancers.