ROLACTIN appears to have a major role in the growth, P development, and function of the human breast' as well as in the initiation and propagation of mammary cancer in rodents.* In humans, too, there is now some published evidence which incriminates high circulating prolactin levels to poor prognosis both in early and advanced breast ~a r c i n o m a .~-~ Studies on have also demonstrated the correlation between high prolactin receptor levels to a shorter survival. These and other studies",'* point toward a significant role for prolactin in the pathogenesis of human breast carcinoma.In a recent unpublished study' we found that prolactin had a linear correlation with histologic grade and an inverse correlation with (1) estrogen receptor and progesterone receptor levels, and (2) survival. The current study addresses the following issues: (1) relation between the changes in serial plasma prolactin and disease status; and (2) existence of lead time (if any) from a rise in prolactin level to the appearance of recurrence of disease. Materials and Methods PatientsOne hundred forty-four female breast cancer patients treated at the Gujarat Cancer and Research Institute, Ahmedabad, India, were included in the study between September 1984 and May 1988. They were grouped as premenopausal (N = 64) and postmenopausal (N = 80). Agematched healthy controls of either menopausal groups (N = 30 each) were also examined. Patients and controls were considered postmenopausal who had ceased menstruating for 5 or more years. Perimenopausal patients and controls (within 5 years of menopause) were excluded from the study. Blood samples were collected in ethylenediamine tetraacetic acid (EDTA), disodium salt ( 1-2 mg/ml)-coated tubes for prolactin estimation between 9.0 and 11.0 AM preoperatively and at monthly intervals thereafter. The plasma was separated within 1 to 2 hours and stored at -70°C. until assayed, usually within 1 month.