Is breast-conserving therapy a safe option for patients with tumor multicentricity and multifocality?

Background: We compared outcomes after breast-conserving therapy (BCT) and mastectomy in multicentric (MC)/multifocal (MF) versus unifocal breast cancer. Patients and methods: Women with stage I-II disease were classified as having unifocal or MC/MF disease. MC/MF and other prognostic factors were compared using binary logistic regression analysis. Univariate and multivariate analyses (MVAs) for relapse were carried out using cumulative incidence curves and Fine and Gray regression models. For the BCT group, matched analysis was added. Results: Median follow-up was 7.9 years, 11 983 having BCT (unifocal: 11 683, MC/MF: 300) and 7771 having mastectomy (unifocal: 6884, MC/MF: 887). MC/MF patients treated with BCT were 50-69 years old, free of extensive ductal carcinoma in situ (DCIS), and had smaller tumors. The cumulative 10-year local recurrence rates among unifocal and MC/MF disease were 4.6% [95% confidence interval (CI) 4.1% to 5.0%] versus 5.5% (95% CI 2.6% to 9.9%) for the BCT group, P = 0.76 and 5.8% (95% CI 5.2% to 6.5%) versus 6.5% (95% CI 4.7% to 8.7%) for the mastectomy group, P = 0.77. MC/MF was not a significant factor for relapse or survival on MVA. In the matched analysis, relapse rates were similar in the unifocal and MC/MF groups, P = 0.60. Conclusion: BCT is a reasonable option in selected MC/MF cases, particularly those women aged 50-69 years old with small (<1 cm) MF tumors and without an extensive DCIS component.