Biological and histological characteristics of simultaneous bilateral breast cancer.

Biological and histological characteristics of simultaneous bilateral breast cancers were studied in 11 patients: 8 had bilateral oestrogen receptor (ER)-positive tumours, 2 had bilateral ER-negative tumours; and only 1 case was asymmetric in receptor status. In contrast 5 of 7 asynchronous bilateral tumours demonstrated disparity in receptor status. The high incidence of bilateral positivity and similarity of receptor content in the simultaneous group suggests that the development of this group of tumours is probably hormonally related. Furthermore, the inverse relationship between tumour size and receptor content suggests an alteration in tumour characteristics during tumour progression.