Can plasma prolactin predict tamoxifen resistance in patients with advanced breast cancer?

The antiestrogen tamoxifen (TAM) is an effective therapy for advanced breast cancer. However, its use is limited by the eventual development of acquired TAM resistance in many patients. There is now strong evidence to suggest that prolactin plays an important role in advanced breast cancer. We have measured plasma prolactin (PRL) and estrogen-receptor (ER) and progesterone-receptor (PR) in post-menopausal patients with breast cancer (Stage III, n = 44). The blood samples were collected pre-operatively and sequentially thereafter for a minimum period of 3 years or until the death of the patients. The ER and PR were estimated in breast tumor samples by dextran-coated charcoal (DCC) method. The patients were treated with surgery and radiotherapy followed by TAM (10 mg, 1 BD). Based on the response to treatments, the patients were divided into two groups: (1) TAM sensitive (n = 19) and (2) TAM resistant (n = 25). In the TAM sensitive group, patients responded to the treatment and did not develop progressive disease within a period of 3 years. On the contrary, in the group of TAM resistant, patients developed progressive disease within a period of 3 years. The development of progressive disease clearly indicated TAM resistance. Plasma PRL correlated well with the disease progression. This study clearly demonstrated that plasma prolactin accurately indicated the response and development of resistance to TAM in patients with advanced breast cancer.