AB037. SOH25_AB_294. Five-year outcomes of local recurrence and distant metastases following mastectomy, stratified by margin status

Background: It is well known that positive margins at breast conserving surgery are associated with higher local recurrence rates. However, the implication of positive margins after mastectomy are less well studied. We aimed to review the five-year local recurrence and distant metastasis rate after mastectomy for those with positive surgical margins.

Methods: A retrospective review of 262 patients undergoing mastectomy for invasive carcinoma or ductal carcinoma in situ (DCIS) between 2016 and 2017 at a single tertiary referral centre was performed. Patients were categorized based on margin status. Variables assessed included tumour stage and subtype, margin status, adjuvant therapy, five-year recurrence rates and metastases development.

Results: Of 262 patients included, 234 underwent mastectomy for invasive disease and 28 for DCIS. Altogether, 33 patients (12.6%) had positive margins. A total of 10 patients (3.8%) developed local recurrence within 5 years, 3% (n=1) of those with positive margins compared to 3.9% (n=9) of those without. A total of 44 (16.7%) patients developed distant metastases within 5 years, 15% (n=5) with positive margins compared to 17% (n=39) without. Fifteen patients had adjuvant radiotherapy for positive margins alone, of whom none developed local recurrence. Patients with positive margins who did not receive radiotherapy for any reason had an 8.3% recurrence rate (1/12).

Conclusions: Positive surgical margins after mastectomy do not appear to be associated with increased recurrence and metastases within five years. However, adjuvant radiotherapy may provide a protective effect. Margin status after mastectomy should be considered when planning adjuvant therapies.

Keywords: Adjuvant radiotherapy; local recurrence; mastectomy; metastases; positive surgical margins