Expression of the estrogen receptor (ER), the progesterone receptor (PgR) or the human epidermal growth factor receptor-2 (HER2) in tumors is a good prognostic marker for breast cancer patients. However, approximately 15-20% of breast cancer patients have triple-negative breast cancer (TNBC; negative for ER, PgR and HER2), and efficient therapeutic modalities for these patients are under investigation. We focused on thymidine phosphorylase (TP), an enzyme metabolizing 5'-DFUR, an intermediate of capecitabine, to 5-fluorouracil in order to investigate the application of well-known therapeutics for TNBC. Results of a gene expression analysis showed that TP expression in TNBC and basal-like breast cancer (BLBC) was higher than that of other subtypes. Immunohistochemically, the high expression of TP in TNBC and BLBC reflected expression in stromal but not tumor cells. Notably, a high TP expression was observed in the stromal cells of EGFR- and/or CK5/6-positive breast tumors. Our present results showing a high expression of TP in BLBC indicate that capecitabine-based chemotherapy would be of benefit for patients with TNBC.

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