Coincidence of chronic lymphocytic leukaemia with Merkel cell carcinoma: deletion of the RB1 gene in both tumors.

The authors report a case of a 64-year-old man with chronic lymphocytic leukaemia (CLL) diagnosed 5 years ago. Recently, the patient was admitted with a tumour of the skin in the left lumbar region. Histological and immunohistochemical examinations established the diagnosis of Merkel cell carcinoma (MCC). Electron-microscopic examination revealed the formation of spherical aggregates of intermediate-sized filaments in the perinuclear region. The coincidence of MCC and CLl is rather rare and in published cases, no cytogenetic examinations were performed. We examined the RB1 gene using the interphase FISH method. A biallelic deletion in CLL tumour cells was detected; in MCC tumour cells, biallelic deletion was found in 33% of the cells and monoallelic deletion in 57% of the cells. In addition, chromosome 6 trisomy and 1p36 deletion were detected. Examination of non-neoplastic cells of the patient's skin showed a biallelic presence of the RB1 gene. According to the relevant literature, examination of the RB1 gene in CLL has informational value as a prognostic factor. The relationship between deletion of the RB1 gene and prognosis in MCC has not yet been determined and needs more research.