365 Completion Mastectomy After Wide Local Excision (Wle) and Sentinel Lymph Node Biopsy (Slnb) for Ductal Carcinoma Insitu (Dcis), Local Data from the Countess of Chester Hospital

Abstract Aim We looked at patients undergoing SLNB at time of completion mastectomy for DCIS to identify the incidence of microinvasion, invasive carcinoma and positive SLNB following completion mastectomy for DCIS. Method Retrospective study on a cohort group of patients who underwent completion mastectomy after WLE for DCIS for positive or close margins in the period from January 2010 to December 2021. Exclusion criteria were invasive cancer or microinvasion identified on the WLE specimen, previous ipsilateral breast cancer and recurrent cases who underwent upfront mastectomy after previous WLE for DCIS. The main limitation of the study was the limited number of cases that fit the inclusion criteria of the study in a single institution. Results Total 30 cases were identified that fit the inclusion criteria of the study. SLNB was performed in 25 cases (17 cases with completion mastectomy and 8 cases with WLE). Only 5 cases, did not have SLNB. None of the studied cases showed microinvasion or invasive cancer in the final pathology in the mastectomy specimen. None of the SLNB performed was positive. Conclusions In view of the final mastectomy specimen showing no microinvasion or invasive cancer, combined with all SLNB results being negative, it can be posited that a significant portion of the abnormality had already been sampled in the prior WLE. Therefore, the routine use of SLNB during completion mastectomy is questionable. We would like to continue this audit prospectively and collaborate with our joint screening unit to obtain more meaningful results to support change in local practise.