PB.40. What happens to the ductal carcinoma in situ in HER2-positive cancers treated with neoadjuvant chemotherapy and trastuzumab?

There are few data regarding the effect of neoadjuvant chemotherapy (NACT) and trastuzumab on any ductal carcinoma in situ (DCIS) associated with the HER2-positive invasive carcinoma. HER2-positive breast cancers are more likely to achieve a pathological complete response (defined as absence of invasive tumour in the final excision specimen allowing for the presence of DCIS). We review our data to see what happens to HER2-positive DCIS associated with HER2-positive invasive cancer treated with NACT.

All cases that were HER2-positive from our local NACT database were identified from 2010 to 2012. The imaging features, core biopsy and final histology were documented

A total 41 of 150 patients that received NACT (anthracycline and taxane based) were HER2-positive and treated with trastuzumab. In total, 40/41 cases had surgery following neoadjuvant treatment, 24/41 (59%) cases had calcifications on mammography, and 21/41 (51%) obtained a pCR. Of the 24 cases with calcification, 14 (44%) had a pCR with 9/14 (29%) having residual DCIS. Seven of 24 cases had a WLE in which the calcifications on mammography were unchanged in extent or appearance. A total 17/41 were without calcification, seven (57%) had a pCR with 2/7 (62%) having residual DCIS that was noncalcified.

pCR is higher in the HER2-positive group compared with the HER2-negative group (51% vs. 20%). In total, 48% achieved a pCR with no residual DCIS but 52% still had residual DCIS, suggesting that trastuzumab may be less effective in treating HER2-positive DCIS.