ESR1 and breast carcinoma: Next, three TNBC cell lines (MDA-MB-468, MDA-MB-436 and MDA-MB-231), ER(+) breast cancer cell line (MCF7) and HER2(+) breast cancer cell line (SK-BR-3) were used to analyze PTK7 expression and the result showed significantly higher PTK7 levels in TNBC cells than that in MCF7 and SK-BR-3 cells (data not shown).