Increased incidence of chronic lymphocytic leukaemia and lymphomas in patients with Merkel cell carcinoma - a population based study of 335 cases with neuroendocrine skin tumour.

Merkel cell carcinoma (MCC) is a rare aggressive skin tumour that appears to be associated with a large number of other tumours. We collected all reported cases in Israel and estimated its association with other tumours, including haematological malignancies. The population based Israel Cancer Registry identified 335 patients with MCC diagnosed between1989 and 2010. Ninety-seven percent were in the Jewish population; median age at diagnosis for Jewish patients was 73·4 and 55·6 years for the Arab population. Other associated malignancies were encountered in 92 patients (27·4%) with MCC (90 Jews, two Arabs). Of the Jewish cases, 66 presented with an associated malignancy before, and 24 after, the diagnosis of MCC. Solid tumours were not significantly increased among patients with MCC. Thirty-one of these associated cancers (34·4%) were haemato-oncological malignancies, 24 were detected before and seven after the diagnosis of MCC. The standardized incidence ratio (SIR) for haematological malignancy was 3·67 for males and 3·62 for females, and the most frequent haemato-oncological neoplasias recorded were chronic lymphocytic leukaemia (45%) and lymphomas (29%). Although MCC is rare, clinicians should be aware of the possible association with B-cell lymphoproliferative disorders when evaluating patients with neuroendocrine skin tumours.