ESR1 and breast cancer: Using a case series of breast cancer patients built following the REMARK recommendations for tumor marker prognostic studies [22] (Table S8 in File S1), membrane Trop-2 was shown to be associated with major determinants of biological history of breast cancer, i.e. membrane Trop-1 and CD44v, with ERα/PgR-negative cases, and with distinct breast cancer subgroups (luminal, triple negative).