Bilateral/contralateral prophylactic mastectomy (PM) is offered to high-risk women to decrease their actual or perceived breast cancer risk. When an invasive occult cancer is identified, prevailing wisdom suggests that an axillary dissection be performed. This single-institution study aims to identify patients who may benefit from sentinel node biopsy (SLNB) at the time of prophylactic mastectomy.

We performed a retrospective review of a prospective database of patients treated at our institution with bilateral/contralateral PM between 1995 and 2006. We examined patients' clinicopathologic characteristics in comparison with their incidence of occult cancer in the contralateral breast or axilla.

There were 449 patients who underwent PM and SLNB. Twenty-eight underwent bilateral PM. Of the 28, no occult cancers were identified. Occult cancers were identified in 18 of 420 (4.3%) contralateral prophylactic specimens; they were invasive in 6 (1.4%). In cases of occult carcinoma, the primary established tumor was more likely to be of invasive lobular histology. Eight of 420 (2%) patients had a positive contralateral sentinel node, and within this subset of 8 patients the majority had locally advanced disease on the known tumor side. Other features associated with a positive contralateral sentinel node included the presence of lymphovascular involvement or skin or nipple involvement and grade 2 to 3 invasive primary established tumors.

Overall, SLNB in patients undergoing bilateral PM or contralateral PM associated with early-stage disease is not indicated. But patients with locally advanced primary breast cancers have a significantly increased risk of occult cancer in the contralateral axilla, likely due to crossover metastasis; this select group of patients may benefit from SLNB at the time of surgery.