ESR1 and breast cancer: While the averages of SPINT1 and SPINT2 expression levels are not different in the cancer stages I–II and III–IV (Figure 2A), SPINT2 expression levels were somewhat lower in ER− and TN breast cancer groups (Mean differences of SPINT2, ER− vs. ER+, P < 0.01, TN vs. luminal A, P < 0.01, TN vs. luminal B, P < 0.01, TN vs. HER2.