The superficial margin of the skin-sparing mastectomy for breast carcinoma: factors predicting involvement and efficacy of additional margin sampling.

BACKGROUND: No study has systematically evaluated the significance of involvement of the superficial specimen margin in skin-sparing mastectomies (SSMs).
METHODS: 168 SSMs with a small, additional superficial margin (ASM) specimen taken directly over the tumor to the dermis intraoperatively were studied.
RESULTS: 64 SSMs (38%) had a positive superficial specimen margin but only 13 (20%) of these had residual breast carcinoma in ASMs. Only 1 of 104 SSMs with a negative superficial specimen margin had residual breast carcinoma in its ASM (P < 0.05). ASM sampling rendered the final true margin directly over the tumor negative in 54 of 58 (93%) SSMs with a focally positive superficial specimen margin, but did not negate the nonfocally positive superficial specimen margin in six other cases. In SSMs with a positive superficial specimen margin, multivariate analysis revealed that the presence of extensive ductal carcinoma in situ (DCIS) in the SSM and a thicker ASM specimen were the only independent factors predictive of residual breast carcinoma in ASM. Eighty-nine (53%) ASMs contained benign breast tissue.
CONCLUSIONS: Superficial specimen margins in SSMs are often microscopically positive and approximately half of ASMs contain benign breast tissue, likely reflecting the difficulty in completely removing breast tissue near the skin flaps in SSMs. ASM sampling effectively decreases positive superficial specimen margins directly over the tumor in SSMs, but fails to account for positive superficial specimen margins in other quadrants in patients with multicentric disease, especially extensive DCIS. Patients whose superficial margins remain positive could potentially represent a subset of patients for whom postmastectomy radiation is beneficial.