Evaluation of clinical significance of basal-like subtype of breast cancer identified by immunohistochemistry

Abstract

21107 Background: At present time, prognostic evaluation of initial breast cancer is mostly based on patients’ clinical and tumoral histological features. Recently, molecular subtypes of invasive breast cancer were recognized through DNA microarray profiling studies. This new classification can potentially improve the prognostic evaluation but this technology is still not widely available. The possibility of identifying the molecular subtypes through simpler and cheaper methods is promising. The identification of basal-like breast cancer (BLBC) is particularly important because it has a poor outcome and fewer treatment options available. Additionally, Epidermal Growth Factor Receptor (EGFR) expression seems to be more frequent in this subtype. Methods: A retrospective cohort of 112 consecutive patients with pathologic stage I or II primary breast carcinomas, treated in the same institution between 1995 and 2000, was studied. Histological and clinical features as well as clinical outcome and survival were reviewed. Immunohistochemical analysis was carried out in representative blocks of tumors with antibodies against Estrogen Receptor (ER), Human Epidermal Growth Receptor - type 2 (HER2), CK5/6 and EGFR. The primary endpoint was to determine the prevalence of BLBC (ER and HER2-negative and CK 5/6 and/or EGFR-positive) in this population. Results: 13 of 112 tumors (11,6 %) were BLBC. Their mean age was 49 years; 77 % were stage II and 100 % were invasive ductal carcinomas. There was no prognostic difference between BLBC and the subtypes luminal (ER-positive and HER2-negative); HER2-overexpressing (HER2-positive) and undetermined (four markers negative) relating to disease-free and overall survival. This is probably related to limited number of patients in this study and good prognosis of initial-stage patients. 11 of 112 cases (10%) were positive for EGFR. EGFR-positive tumors tended to be ER- negative (23 % vs 5 %; p=0,01). Conclusions: Our results suggest that it is possible to identify BLBC by immunohistochemical analysis of ER, HER2, CK 5/6 and EGFR. Besides, EGFR expression seems to be more frequent in ER-negative tumors, which suggest EGFR-targeted drugs may benefit this population. No significant financial relationships to disclose.