ESR1 and breast carcinoma: In addition, 6q15 deletions were significantly linked to the subset of estrogen receptor (ER) negative breast cancers: deletion was found in 24% of ER negative but only in 17% of ER-positive breast cancers (p = 0.0182) and to the molecular subtypes of HER2-positive and basal cell type cancers (p = 0.0062).