Leptin is a protein produced by fat tissue. It has many regulatory effects in the area of energetic metabolism, immunity and haematopoiesis. Its role in tumour diseases especially in states with cachexia is studied. Its physiological diurnal rhythm is very well known. There is lack of information about diurnal rhythm of leptin in tumour diseases except some endocrine tumours. In this study 10 patients with breast and colorectal cancer without marks of kachexia and mostly without pre-existing chemotherapy were examined. The diurnal rythm of leptin was preserved in cancer patients (morning minimum 10.5 ± 4.2 ng/ml and nocturnal maximum17.9 ± 10.1 ng/ml). The difference between males and females (p < 0.01) and correlation of concentrations of leptin with BMI (r = 0.61, p < 0.001) were preserved too. Basal concentrations of leptin were not different from values of healthy blood donors (10.2 ± 4.3 ng/ml). Maybe preservation of diurnal rhythm of leptin can be important in planning of cytostatic and immunomodulatory therapy in future.

        Key words: Leptin - Diurnal rhythm - Malignant tumours