The diagnostic of tumor cells circulating in blood is one of most perspective and actively developing directions in cytology. The most of proposed techniques for this purpose are based on using immune cytochemical or molecular genetic modes to characterize cells. At the samne time, growing spread receives technique of separation of circulating tumor cells based on their larger size in comparison with other blood cells (ISET). The article presents clinical monitoring of application of mentioned technique to verify diagnosis and onset of treatment in female patient with reiterated ineffective diagnostic punctures of pancreas.