Abstract P6-08-44: Impact of the immunohistochemical subtypes of breast cancer on prediction of axillary metastasis: Experience of one breast center in Argentina

INTRODUCTION Axillary node metastasis is one of the most important prognostic factors to be considered in the treatment of Breast Cancer. Although the association between axillary metastasis and pathologic tumor size has been extensively studied, the correlation between the immunohistochemical (IHC) subtype and axillary compromise has not. The aim of this study was to evaluate the correlation between the immunohistochemical subtype of Breast Cancer (BC) and axillary extension. As secondary outcomes, we assessed disease-free (DFS) and overall survival (OS). MATRERIALS AND METHODS 1413 consecutive patients who underwent surgery for invasive primary breast cancer at the Hospital Italiano de Buenos Aires between the years of 2007 and 2012 were included. Patients presenting with stage IV disease were excluded. We analyzed the clinical and pathologic data of patients who were submitted to either sentinel node biopsy (SNB) or axillary lymph node dissection (ALND). Based on IHC, tumors were classified into four groups: Luminal A (RE+ RP+ HER2-, KI 67 15%), HER 2 (RE- RP- HER+) and Triple Negative (TNBC) breast cancer (RE- RP- HER-). RESULTS We evaluated 1413 patients, among which 1248 patients were eligible for inclusion and analysis. In this population, 386 patients (31%) had axillary metastasis. By considering the Luminal A subtype population as our control group, we found that axillary metastasis was significantly increased in the Luminal B and HER2 positive subtypes (p 0.000), and OR 2.05 (CI95% 1.13 -3.70, P=0.017) respectively. In the case of HER2 positive tumors, the odds ratio for axillary extension was 6.62 (CI95% 3.02 - 14.50, P > 0.000). The median follow-up was 29 months (17- 44 months), and the overall survival estimated by Kaplan-Meier was 91% (CI95% 87-94), with a disease-free survival of 62% (CI95% 28-83). DISCUSSION In this cohort, immunohistochemical subtype was an important independent predictor of axillary metastasis. Tumors smaller than 2 cm, that overexpress HER2 in absence of estrogen and progesterone receptor, have up to six times greater incidence of axillary extension than those belonging to the Luminal A subtype. Luminal B and Triple Negative cancers on the other hand appear to present twice the risk when compared to the Luminal A subtype. Citation Format: Maria F Calvo, Carola Allemand, Francisco H Corrao, Roberto Orti, Liliana B Zamora, Maria C Riggi, Maria F Ilzarbe, Jorge Piccolini, Alejandra Wernicke, Sebastian Gogorza, Gustavo Izbizky, Claudio Lorusso. Impact of the immunohistochemical subtypes of breast cancer on prediction of axillary metastasis: Experience of one breast center in Argentina [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-08-44.