To investigate the deviation of survival curves from monotonous shape, 17 curves for 6 most common cancer sites of 87,205 patients (aged 30-89) were selected from The U.S. Surveillance, Epidemiology and End Results (SEER) Register database. The curves were analyzed using monotonous exponential and harmonic functions which allowed a corresponding estimation of quasi-sinusoidal disturbances of monthly death hazard. Detectable fluctuations of the latter were established in the 0-40--month life span zone depending on tumor site and age at diagnosis.