Human breast carcinoma cell levels of MDR-1 (P-glycoprotein) transcripts correlate in vivo inversely and reciprocally with tumor progesterone receptor content.

Sixteen human breast carcinomas were subjected to molecular biological and biochemical analyses to determine tumor cell MDR-1 (P-glycoprotein) levels and progesterone receptor content. The results of these analyses disclosed a strong reciprocal and inverse correlation between levels of tumor cell-specific MDR-1 complementary hybrids and progesterone receptor content. These results suggest that the mechanisms which control expression of the P-glycoprotein gene and the progesterone receptor are interrelated and antagonistic, a result with obvious molecular biological, physiological, and clinical implications.