Serum Cytokeratin 18 as a Metastatic and Therapeutic Marker for Extramammary Paget's Disease.

Extramammary Paget's disease (EMPD) is a rare cutaneous adenocarcinoma with unfavourable prognosis once it becomes invasive. A tumour marker that reflects disease progression is required for adequate management of EMPD. Cytokeratin 18 is highly expressed in many types of cancer and its soluble forms are detected by M30 (for caspase-cleaved form) and M65 (for both caspase-cleaved and intact forms) assays. We report here that tumour cells of EMPD in both lesional skin and lymph node metastasis are immunohistochemically positive for CK18, and the baseline serum M30 and M65 levels in patients with metastatic EMPD are significantly higher than those in non-metastatic patients. In addition, serial serum M30 and M65 levels might reflect recurrence of EMPD and response to chemotherapy. These results suggest that serum CK18 levels may be a useful tumour marker for advanced EMPD.