Mammary cancer risk: circulating TSH and prolactin, fibrocystic breast disease in chronoepidemiologic perspective.

Classical epidemiology associates human breast cancer with several risk factors including, among others, so-called preclinical hypothyroidism, fibrocystic disease of the breast (FM), and hyperprolactinemia. Relationships among FM, hyperprolactinemia, and thyroid function are of interest because of the possibility of multiple risk combinations. Prolactin and TSH (the latter as a presumed index of preclinical hypothyroidism) undergo rhythmic changes and hence should be chronobiologically investigated. Serum samples obtained at 4-hour intervals throughout a 24-hour span from 23 healthy women and from 25 women with FM (histologically verified) here summarized suggest that circadian mesor-hyperprolactinemia is a feature associated with FM. In a broader context, however, such impressions and an often considered modest impairment of thyroid function in some patients must be viewed in the light of new chronobiologic rules. These include a reciprocity of the circannual amplitudes of TSH and prolactin in relation to breast cancer risk, revealed by cooperative studies. A yet broader chronoepidemiologic view reveals that the reciprocal relation of the circannual amplitudes of circulating TSH and prolactin is (sex) inverted in patients with cancer of the prostate.