ESR1 and breast cancer: In grouped analysis for PTK7 expression in ER/PR/HER2-negative (TNBC) vs. ER/PR/Her2-positive BC there was a tendency for higher expression in TNBC, but was not statistically significant due to a small sample size of TNBC (n = 14) and ER/PR/Her2-positive (n = 6) cohort (mean difference −1.55, 95% CI: −3.36 to 0.25, p = 0.083, t-test).