Prognostic significance of tumour-infiltrating lymphocytes for oestrogen receptor-negative breast cancer without lymph node metastasis

Tumour-infiltrating lymphocytes (TILs) are regarded as significant prognostic markers in patients with breast cancer. However, the prognostic utility of TIL expression based on the intrinsic subtypes has just been identified. The present study investigated the relationship between TIL grades and prognosis in 294 Japanese paitents with breast cancer stratified based on the intrinsic subtypes and clinicopathological characteristics. Stromal TIL status was evaluated using haematoxylin and eosin staining, and TIL grades were categorised into low (<10%), intermediate (≥10 and ≤40%) and high (>40%) groups. The relationship between TIL expression and the intrinsic subtypes, clinicopathological characteristics and patient prognosis was analyzed. It was revealed that high TIL expression was correlated with negative oestrogen receptor (ER) expression and high histological grade (P<0.001). Among the ER-negative patients, the relapse-free survival (RFS) rate of the high-grade TIL group was significantly higher than that of the low-grade TIL group (P=0.04). Among the ER-negative patients without lymph node metastasis, RFS and cancer-specific survival (CSS) rates of patients with high-grade TILs were significantly higher than the RFS and CSS rates of patients with low-grade TILs (P=0.01). However, among ER-positive patients, RFS was significantly higher in the low-grade TIL group than in the high-grade TIL group (P=0.02). In conclusion, TIL expression correlated with ER status and tumour proliferation. High TIL expression was a poor prognostic marker in ER-positive patients but was a good prognostic marker in ER-negative patients. Therefore, the biological association between TILs and primary breast tumours may differ between ER-positive and ER-negative breast cancer.