Abstract
Circulating tumor cells (CTCs) are a promising biomarker for several cancers. We streamlined the experimental procedure of CTC immunofluorescent staining. We encountered a 72-year-old woman with metastatic right renal cell carcinoma (RCC) (clinical stage: T4N0M1), whose CTC number rapidly increased after the administration of sunitinib and then gradually decreased. The change in the CTC number appeared to coincide with laboratory data and hypertension, suggesting that a CTC analysis may be useful for promptly monitoring the treatment response. Our data provided the first evidence of an association between the CTC numbers and the treatment response in a metastatic RCC patient.