• Tari A King, Melissa Pilewskie, Shirin Muhsen, Sujata Patil, Starr K Mautner, Anna Park, Sabine Oskar, Elena Guerini-Rocco, Camilla Boafo, Jessica C Gooch, Marina De Brot, Jorge S Reis-Filho, Mary Morrogh, Victor P Andrade, Rita A Sakr, and Monica Morrow.
• All authors: Memorial Sloan Kettering Cancer Center, New York, NY. tking7@partners.org.
• J. Clin. Oncol. 2015 Nov 20; 33 (33): 3945-52.

PurposeThe increased breast cancer risk conferred by a diagnosis of lobular carcinoma in situ (LCIS) is poorly understood. Here, we review our 29-year longitudinal experience with LCIS to evaluate factors associated with breast cancer risk.Patients And MethodsPatients participating in surveillance after an LCIS diagnosis are observed in a prospectively maintained database. Comparisons were made among women choosing surveillance, with or without chemoprevention, and those undergoing bilateral prophylactic mastectomies between 1980 and 2009.ResultsOne thousand sixty patients with LCIS without concurrent breast cancer were identified. Median age at LCIS diagnosis was 50 years (range, 27 to 83 years). Fifty-six patients (5%) underwent bilateral prophylactic mastectomy; 1,004 chose surveillance with (n = 173) or without (n = 831) chemoprevention. At a median follow-up of 81 months (range, 6 to 368 months), 150 patients developed 168 breast cancers (63% ipsilateral, 25% contralateral, 12% bilateral), with no dominant histology (ductal carcinoma in situ, 35%; infiltrating ductal carcinoma, 29%; infiltrating lobular carcinoma, 27%; other, 9%). Breast cancer incidence was significantly reduced in women taking chemoprevention (10-year cumulative risk: 7% with chemoprevention; 21% with no chemoprevention; P < .001). In multivariable analysis, chemoprevention was the only clinical factor associated with breast cancer risk (hazard ratio, 0.27; 95% CI, 0.15 to 0.50). In a subgroup nested case-control analysis, volume of disease, which was defined as the ratio of slides with LCIS to total number of slides reviewed, was also associated with breast cancer development (P = .008).ConclusionWe observed a 2% annual incidence of breast cancer among women with LCIS. Common clinical factors used for risk prediction, including age and family history, were not associated with breast cancer risk. The lower breast cancer incidence in women opting for chemoprevention highlights the potential for risk reduction in this population.© 2015 by American Society of Clinical Oncology.

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