Unexpected features of breast cancer subtype.

Background: Gene expression profiling of breast cancers identifies distinct molecular subtypes that affect prognosis. The aim of this study was to determine whether features of tumors especially the risks of lymph node (LN) metastases differ among molecular subtypes.

Methods: Subtypes were classified by immunohistochemical surrogates as luminal A, luminalHer2-, luminalHer2+, TNBC, and HER-2+. Data were obtained from an established, registered database of patients with invasive breast cancer treated at our hospital between July 2012 and October 2014. A total of 929 tumors were classifiable into molecular subtypes.

Results: The distribution of subtypes was luminal A (24.2%), luminalHer2- (27.8%), luminalHer2+ (9.1%), TNBC (21.3%), and HER-2+ (17.5%). Marked differences in age, tumor size, extent of lymph node involvement, and grade were observed among subtypes. On univariate analysis, the LN positivity varied across subtypes with 33.6% in luminal A, 40.3% in luminalHer2-, 37.3% in luminalHer2+, 37.6% in TNBC, and 47.4 % in HER-2+ (p=0.201). There was no significant difference in LN positivity among subtypes. On multivariable analysis, grade and tumor size were independent predictors of LN positivity.

Conclusions: Predictors of LN metastases include higher grade and larger tumor size. Even though breast cancer subtype is not a statistically significant predictor of LN positivity, this information may still be useful in selecting the appropriate therapy in clinical practice.