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Carcinomas of unknown primary origin (CUPs) account for 3%-5% of all malignancies. The majority of CUPs have unfavorable prognosis and are chemoresistant. Predictive biomarkers should be established to improve therapeutic outcomes. Metastatic ability of CUPs may be related to the existence of circulating tumor cells (CTCs).Ten patients diagnosed with CUP visiting the Akita University Hospital participated in this study. CTCs were calculated by the CellSearch system.The present observational study indicates that CTCs were detected in 50% of CUPs, and in 80% chemotherapeutically-naïve cases. Furthermore, decrease in CTC count between the pre-treatment and post-treatment phases were observed in chemosensitive cases.Rapid assessment of the efficacy of chemotherapy by CTC count may become a useful predictive biomarker of CUPs.

Molecular-targeted therapies require the assessment of targets and their related molecules. Circulating tumour cells (CTCs) are considered a very good source of samples for these purposes. In this study, we applied a practical method for examining CTCs to evaluate the effects of chemotherapy on advanced colorectal cancer (CRC). Even in stage IV CRC, CTCs were detected in only 38.5% (n=5/13) of the cases. However, in cases where CTCs were detected, the change in the number of CTCs compared before and after chemotherapy appeared to be associated with the therapeutic outcome. Changes in the number of CTCs may be a good predictive biomarker. Problems with this method are yet to be resolved, including the detection rate and the stability of the sample source for subsequent molecular analysis.