68P When is a Close or Positive Margin Following a Mastectomy an Indication for Chest Wall Radiotherapy in Patients with T1N0 Breast Cancer?

Abstract

BackgroundSince a mastectomy for T1N0 breast cancer generally results in very high rates of local control, radiation oncologists are only consulted when close or positive margins are encountered in this setting. The actual length of margins below which the risk of local failure increases and the rate of local recurrence in this subset of patients is, however, not well defined in the literature. Here we report our experience with these patients in this retrospective analysis. Materials and methodsOf the women who underwent a mastectomy for pT1NO breast cancer from 1994 through 2004 at our institution, 256 had an invasive and in-situ margins of <10mm and were included in this review. The following factors were analyzed for local recurrence: the length of the closest margin, location of closest margin (deep or other), histology (ductal, lobular, other), coexisting DCIS, multifocality or multicentricity, age, type of surgery (simple/skin-sparing/total mastectomy, modified radical mastectomy), grade, lymphovascular invasion, hormone receptor status, adjuvant hormonal therapy, and adjuvant chemotherapy. ResultsMedian follow-up for surviving patients was 7.2 years. Chest wall recurrence was found in 8 patients (3.1%) at a median interval of 2.2 years, one of whom had a simultaneous axillary recurrence. Isolated axillary failure was noted in one patient. The incidence of chest wall recurrence was 6.5% for those with margins ≤3 mm (N = 107) vs 0.7% when margins were >3 mm (P = 0.02). Additionally, 7.9% of those with high-grade disease had a chest wall recurrence compared to 1.1% in those with grades 1-2 (P = 0.01). Among 28 patients with both high-grade disease and margins ≤3 mm, 6 (21%) developed chest wall recurrences. No other factors were found to be predictive of local recurrence. Of note, only one of eleven patients with positive margins had a chest wall recurrence. ConclusionsThis analysis suggests that although postmastectomy patients with T1N0 breast cancer with margins ≤3 mm have an elevated risk of chest wall recurrence, only those with the additional risk factor of high-grade disease appear to have a sufficiently high risk to merit strong consideration of chest wall radiotherapy. DisclosureAll authors have declared no conflicts of interest.