A component of lobular carcinoma in clinically lymph node–negative patients predicts for an increased likelihood of upstaging to pathologic stage III breast cancer

PURPOSE: Physical examination and diagnostic imaging are often less precise in determining the extent of disease in invasive lobular carcinoma (ILC) relative to nonlobular histologies. Anecdotally, surgical axillary evaluation frequently reveals positive lymph nodes in clinically N0 patients with ILC; however, few studies quantify the likelihood of finding unsuspected disease at the time of surgery. In this study, we evaluate whether the presence of lobular histology increases the incidence of surgical upstaging to pathologic stage IIIA or greater in patients with a clinically node-negative axilla and positive sentinel lymph node (SLN) biopsy. METHODS AND MATERIALS: We examined patients from our institution between 1997 and 2009 treated specifically with mastectomy, SLN biopsy, and completion axillary lymph node dissection due to a positive SLN. For analysis, patients were grouped according to the presence of any lobular component on surgical pathology. The number of total positive lymph nodes, cancer stage, age, final tumor size, and ER/PR/HER2 status were assessed based on tumor histology. RESULTS: We evaluated 345 previously untreated women with clinical T0-T2 and N0 disease at the time of surgery. A total of 110 patients (32%) had a component of ILC on surgical pathology. In addition, 295 patients (85.5%) had ER + breast carcinoma, 243 (70.4%) had PR + disease, 56 (16.2%) were HER2 + , and 28 (8.1%) were triple negative. At the time of surgery, women with lobular disease were observed to have a greater number of positive lymph nodes (2.79 vs 2.26; P = .009) and were more frequently upstaged to at least pathologic stage IIIA compared with nonlobular patients (30.9% vs 17.4%; P = .007). CONCLUSIONS: In this cohort, patients with a component of lobular carcinoma were more often surgically upstaged to pathologic stage IIIA or higher, which is a classical indication for postmastectomy radiation therapy. Our findings suggest that ILC is often more extensive than it appears clinically and has significant implications for management of patients with lobular carcinoma after the discovery of a positive SLN.