A population-based study of the effectiveness of breast conservation for newly diagnosed breast cancer

Purpose: Our objective was to evaluate the effectiveness of breast conserva tion for newly diagnosed breast cancer, Effectiveness was operationalized a s two outcomes within 5 years of the diagnosis of breast cancer: the probab ility of mastectomy-free survival (either death or mastectomy count as even t, whichever comes first), and the probability of mastectomy conditional on survival (mastectomy counts as event, observations censored at death), Methods and Materials: We linked records of 46,687 new cases of breast canc er from 1982 to 1991 in the Ontario Cancer Registry to records of surgery f rom 1982 to 1995, radiotherapy (RT) from 1982 to 1992, and median household income from the 1986 census. We labeled breast surgery within 4 months and postoperative RT within 12 months of diagnosis as treatment for newly diag nosed breast cancer, Surgery was categorized as mastectomy, lumpectomy plus RT, lumpectomy alone, or no surgical procedure. Among cases that did not u ndergo mastectomy within 4 months of diagnosis, we labeled mastectomy subse quent to 4 months after diagnosis as treatment failure. We performed life-t able analysis and Cox proportional hazards regression, to describe the prob ability of mastectomy conditional on survival and the probability of mastec tomy-free survival. Results: A total of 16,279 cases underwent lumpectomy as the maximum proced ure on the breast within 4 months of diagnosis, and 49.7% of these received postoperative RT, Compared to the provincial mean, regions with higher rat es of lumpectomy plus RT have higher probability of mastectomy-free surviva l and lower probability of mastectomy conditional upon survival 5 years aft er diagnosis of breast cancer. Conclusions: These findings are consistent with a hypothesis that breast co nservation is effective in the overall breast cancer population of Ontario within the first 5 years after diagnosis. (C) 2000 Elsevier Science Inc.