e14005 Background: Cutaneous melanoma (CM), breast cancer (BC) and lung cancer (LC) metastasize to the brain most frequently. Early diagnosis of cerebral metastases is challenging and requires new prognostic criteria. Imbalance of thyroid and glucocorticoid hormones changes the growth and development of malignant tumors. The purpose of the study was to identify readily available prognostic criteria for cerebral metastases in cancer patients at various stages of treatment and follow-up. Methods: Blood levels of cortisol and total triiodothyronine (tT3) were determined by RIA (Immunotech, Czech Republic) in patients with BC (n = 50), LC (n = 50) and CM (n = 50) without brain metastases and in patients with BC (n = 25), LC (n = 25) and CM (n = 25) with cerebral metastases. Results: Blood levels of cortisol in BC, LC and CM patients were normal in 63-84% and elevated on average by 1.7 times in 16-37%. Levels of tT3 in LC were normal, and in BC and CM – within the normal limits, but 1.3 times lower than the mean values. In patients with cerebral metastases, cortisol was lower than the norm by 4.9, 2.5 and 3.6 times in 36% BC, 75% LC and 45% CM cases, respectively. Levels of tT3 in all patients with cerebral metastases were lower than the norm or values in patients without metastases by 2 times and lower. Conclusions: Decreased levels of both cortisol and tT3 in patients with BC, LC and CM may serve as one of prognostic markers of possible development of cerebral metastases. The dynamic determination of levels of thyroid and glucocorticoid hormones is required in cancer patients at various stages of treatment and follow-up.