P4-09-34: Luminal Infiltrating Lobular Carcinoma of the Breast: Clinical and Prognostic Features.

Abstract

Abstract Background Infiltrating lobular carcinoma (ILC) and infiltrating ductal carcinoma (IDC) are the two most common histologic types of invasive breast cancer. Previous studies have demonstrated distinctive clinical and biologic characteristics, however some features of ILC are yet uncertain like the relationship with the particular subtypes according to the gene expression profile. The purpose of our study is to analyze how the patients with ILC differ from IDC regarding of percentage of luminal subtype, the tumor factors, treatment and patterns of recurrence. Patients and Methods We assessed 1190 breast cancer patients treated at the Hospital Universitario 12 de Octubre between 1995 and 2006 categorized as having ILC or IDC pure types. Results: One thousand one hundred ninety tumors were included, being ILC 223 patients (18, 7%), IDC 967 patients (81, 3%) and 200 patients (10%) were luminal HER2+. The current analysis is limited to the 990 patients classified as luminal HER2−. Median age was 59, 2 years for ILC and 58, 8 for IDC, with no significant differences among the groups. Compared to IDC, ILC showed a larger tumor size (≥T3: 15, 2% vs. 4, 8%, ***p<0.01), lesser nodal involvement (35% vs 42, 7% p 0.048) and lower Ki67 expression (62, 6% vs. 52, 2% p=0.01). The proportion of luminal A subtype was greater in ILC (56, 3% vs. 46, 7% p=0.01). Mastectomy was more frequently performed for ILC (61, 2 % vs. 47, 7%, p=0.01). Regarding systemic therapy, 127(62,4%) ILC patients and 450 (57, 2%) IDC patients received adjuvant chemotherapy (QT). That was anthracycline-based in most cases (47, 2% for ILC and 46,4% for IDC). Adjuvant hormonal treatment was prescribed equally among both groups (196, 96% ILC and 739, 94% IDC), being the most commonly used drug ***tamoxifen. With a median follow-up of 94 months, 45 ILC patients (22%) and 159(20, 2%) IDC relapsed. No differences were observed in DFS (p=0, 81) or OS (p=0, 47). The most frequent metastatic site was bone (33% for ILC and 40, 8% for IDC), followed by local relapses (17, 7% for ILC vs. 17% for IDC) and liver (15, 5% for ILC vs. 15, 7% for IDC). ILC was associated with an increased incidence of peritoneal/mesenteric metastases (8 pts 17, 7% vs. 1pts 0,6% ***p<0.01) and a lower incidence of lung relapses (8, 8% vs. 19, 4 % pts p<0.05). Conclusion: Luminal HER2− Infiltrating lobular carcinoma carries distinct clinicopathological features. In our study, ILC had similar prognosis as IDC. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-09-34.