A unique case of merkel cell carcinoma and chronic lymphocytic leukaemia presenting in a single cutaneous lesion (collision tumour)

Summary

A 58-year-old man with 10 year history of chronic lymphocytic leukaemia (CLL) presented with a bulging mass (3.2×1.6×1.5 cm) in the right anterior abdominal wall. On microscopic examination the mass was found to be an epithelial neoplasm in the background of lymphoid proliferation. The epithelial cells were of moderate size, with scant cytoplasm and round nuclei, forming glandular, alveolar or sheet-like structures. These cells were immunoreactive for cytokeratin 20, chromogranin and synaptophysin. The above findings supported a diagnosis of Merkel cell carcinoma (MCC). The background small lymphocytes expressed phenotypic markers of B cells (CD20) and CD5, consistent with his known diagnosis of CLL. The incidence of a patient with a known history of CLL who develops a secondary MCC is rare. This is believed to be the second case report of a single lesion containing CLL and MCC.