Breast Conservation and Negative Margins in Invasive Lobular Carcinoma: The Impact of Oncoplastic Surgery and Shave Margins in 358 Patients

Invasive lobular carcinoma (ILC) of the breast grows in a diffuse pattern, making complete surgical excision difficult. This results in high rates of positive margins and low rates of successful breast-conserving surgery. We hypothesized that utilizing oncoplastic surgical techniques and selective shave margins would be associated with lower positive margin rates and increased breast conservation in women with ILC. We performed a retrospective cross-sectional analysis in a large cohort of prospectively collected ILC cases who received surgical treatment at the University of California, San Francisco, between 1992 and 2017. We identified all patients with histologically proven, unilateral or bilateral, stage 1-3 ILC. The primary outcome was positive margin rates, defined as no ink on tumor. We identified 365 tumors in 358 women, with an average age of 61 years, who underwent breast-conserving surgery, and found that the use of oncoplastic techniques (odds ratio [OR] 0.4, 95% confidence interval [CI] 0.21-0.79, p = 0.008) and the selective use of shave margins (OR 0.393, 95% CI 0.22-0.7, p = 0.002) were significantly associated with lower positive margin rates, when adjusted for tumor size and multifocality. The success rate for breast-conservation surgery was 75%, with a 25% conversion rate to mastectomy. Surgeons should consider routine use of oncoplastic techniques and shave margins when performing breast-conservation surgery for women with ILC as these methods are associated with significantly lower odds of having positive margins and higher breast-conservation rates.