Melatonin in human breast cancer tissue: association with nuclear grade and estrogen receptor status

The pineal hormone melatonin has been reported to inhibit tumor growth in a variety of experimental and clinical situations and to be an important immunoregulatory agent. Cancer patients with mammary or prostate tumors show reduced levels of circulating melatonin. Melatonin might, thus, be involved in the development of the malignant disease and act directly on tumor cells. Melatonin concentration in human neoplastic and adipose tissue sampled from mastectomy or tumorectomy products (n = 15) was measured by high-performance liquid chromatography. Melatonin seemed to be 3 orders of magnitude more concentrated in the neoplastic and adipose tissues of the breast than in sera from healthy subjects or cancer patients. Few samples (n = 3) of normal breast tissues showed equally elevated concentrations of melatonin. Most interestingly, we found a significant inverse correlation between nuclear grade and melatonin concentration (p < 0.006) and a positive association between melatonin and estrogen receptor status (p < 0.02). No correlation between age of the patients and melatonin concentration was evident. Melatonin might be produced in situ by mammary epithelial cells and represent a good prognostic marker. The possibility that exogenous melatonin might influence nuclear grade and/or estrogen receptor activity in breast cancer patients should be investigated.