156 patients with advanced
breast cancer of known
estrogen receptor (ER) and
progesterone receptor (PgR) status treated by endocrine
therapy were studied. Regarding values for ER and PgR greater than or equal to 5 fmole/mg cytosol
protein as positive, patients were divided into 4 phenotypic subgroups: ER+PgR+ (43%), ER+PgR- (26%), ER-PgR+ (8%), and ER-PgR- (23%). In patients with
tumor phenotype ER+PgR+, responses were seen in 20/30 (67%) assessable initial treatments when receptor assays were performed on
tumor recurrence or on primary
tumor immediately before endocrine
therapy, and in only 11/32 (34%) assessable initial treatments when receptor analysis was performed on primary
tumor and there was intervening local
therapy before endocrine
therapy was started for
tumor recurrence (P less than 0.05). Responses to first endocrine
therapy for each
tumor phenotype were ER+PgR+ 50%, ER+PgR- 27%, ER-PgR+ 27%, and ER-PgR- 6%. Four of 16 (25%) patients with ER+PgR+
tumors responded to subsequent secondary endocrine
therapy, but such responses were not observed in 20 patients with other
tumor phenotypes. Duration of response was similar for each phenotype, but patients with ER-PgR-
tumors had a significantly shorter survival from time of initial endocrine treatment than patients of any other phenotype. These results suggest that repeat
steroid receptor assays on accessible
tumor immediately before endocrine
therapy may result in improved predictability.