Impact of intrinsic subtype on predicting axillary lymph node metastasis in breast cancer

Axillary lymph node (LN) metastasis is one of the most important prognostic factors for the survival of breast cancer. The correlation between LN metastasis and the tumor (T) category has previously been investigated in certain case series. At present, the initial treatment approach is to define the intrinsic subtype, as it is significant in determining medical treatments, as well as being a prognostic factor. However, the intrinsic subtype is not known to predict the frequency of LN metastasis. The aim of the present study was to evaluate the frequency of LN metastasis with regard to tumor size according to the intrinsic subtype. In total, 654 patients with primary breast cancer were evaluated who underwent surgical resection between 2010 and 2011 at the Aichi Cancer Center Hospital (Nagoya, Aichi). The clinical and pathological data were analyzed for patients who underwent an axillary LN dissection or a sentinel LN biopsy for primary breast cancer. The intrinsic subtype of the primary tumors was classified using immunohistochemical staining of thin, paraffin-embedded sections. In total, 157 (24.0%) of the 654 patients exhibited LN metastasis, and according to the primary tumor category, a larger tumor size was found to correlate with a higher proportion of LN positivity, as well as with the luminal A subtypes (n=364). In luminal B subtypes (n=110), T1a (n=2), T1b (n=12), T1c (n=55), T2 (n=34), and T3 (n=2) exhibited 50, 8.3, 38.2, 55.9 and 50% LN positivity, respectively. In luminal-human epidermal growth factor receptor 2 (HER2) subtypes (n=46), T1c (n=17), T2 (n=10), and T3 (n=1) exhibited 40.1, 60 and 100% LN positivity, respectively. In HER2 subtypes (n=53), T1a (n=6), T1b (n=4), T1c (n=15), and T2 (n=10) exhibited 16.7, 25, 46.7 and 60% LN positivity, respectively. In triple-negative subtypes (n=81), T1b (n=15), T1c (n=29), T2 (n=20), and T3 (n=2) exhibited 26.7, 24.1, 50 and 50% LN positivity, respectively. In conclusion, the intrinsic subtype is significant in predicting the frequency of LN metastasis with regard to tumor size.