A novel tumour marker RCAS1 in a case of extramammary Paget's disease.

A 66-year-old male, whose primary skin lesion in extramammary Paget's disease had been surgically resected 4 years previously, was hospitalized with liver metastases. Hepatic arterial infusion chemotherapy was carried out and the tumours clearly reduced in size. Serum levels of some common tumour markers were not elevated, even prior to therapy. We measured serum levels of a novel tumour-associated antigen, RCAS1, because its expression was detected in the tumour cells. The patient's serum RCAS1 level was elevated (22.0 U/mL) before therapy and fell during (10.5 U/mL) and after (5.0 U/mL) therapy. Therefore, serum RCAS1 levels may be valuable as a potential biomarker for monitoring therapeutic efficacy against Paget's disease.