Multiple foci of microinvasion is associated with an increased risk of invasive local recurrence in women with ductal carcinoma in situ treated with breast-conserving surgery

Abstract

The impact of Ductal Carcinoma in Situ (DCIS) with multiple foci of microinvasion (MI) (≤\u20091 mm) on the risks of local recurrence (LR) and invasive LR is unknown, leading to uncertainty if DCIS with multiple foci of MI requires more aggressive treatment. We report a population-based analysis of the impact of multiple foci of MI, confirmed by pathology review, on the 15-year risks of LR and invasive LR treated with breast-conserving surgery (BCS)\u2009±\u2009radiotherapy (RT). Cohort includes all women diagnosed with DCIS\u2009±\u2009MI from 1994 to 2003 treated with BCS\u2009±\u2009RT. Cox proportional hazards model was used to evaluate the impact of multiple foci of MI on the risks of LR and invasive LR, adjusting for covariates. The 15-year local and invasive local recurrence-free survival rates were calculated using the Kaplan–Meier method with differences compared by log-rank test. The cohort includes 2988 women treated by BCS; 2721 had pure DCIS (51% received RT), 267 had DCIS with one or more foci of MI (58% had RT). Median follow-up was 13 years. Median age at diagnosis was 58 years. On multivariable analyses, the presence of multiple foci of MI was associated with an increased risk of invasive LR (HR\u2009=\u20091.59, 95% CI 1.01–2.49, p\u2009=\u20090.04) but not DCIS LR (HR\u2009=\u20090.89, 95% CI 0.46, 1.76, p\u2009=\u20090.7). The 15-year invasive LRFS risks for cases with pure DCIS, with 1 focus or multiple foci of MI were 85.7%, 85.6%, 74.7% following treatment by BCS alone, 87.2%, 89.9%, and 77% for those treated with BCS\u2009+\u2009RT without boost and 89.2%, 91.3%, and 95% for women treated with BCS\u2009+\u2009RT and boost. The presence of multiple foci of MI in DCIS is associated with higher 15-year risks of invasive LR after breast-conserving therapy compared to women with pure DCIS but treatment with whole breast and boost RT can mitigate this risk.