Cyclin D1 expression by histiocytes may mimic cyclin D1-positive proliferation centres of chronic lymphocytic leukaemia/small lymphocytic lymphoma.

AIMS: Cyclin D1, generally considered to be absent in chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL), has been reported in the proliferation centres (PCs) of recent CLL/SLL cases. Cyclin D1 immunostaining in CLL/SLL may lead to diagnostic confusion. The objective of this study was to identify the types of stained cells and the impact on diagnosis.

METHODS: Cyclin D1 expression was assessed by immunostaining samples from 46 cases of CLL/SLL. CD68 and double immunostaining with CD20/CyclinD1, CD68/CyclinD1, and CD163/CyclinD1 were then performed in cases of CLL/SLL positive for cyclinD1 in the PCs.

RESULTS: Dim-positive cyclin D1 staining in randomly scattered cells in the CLL/SLLs were observed in 38/46 cases (82.6%). In five (10.9%) cases, more than 50 cyclin D1-positive cells per high-power field were detected within the PCs in CLL/SLL with weak to moderate intensity. Double immunochemical staining in these cases showed that cyclin D1 in these positive cells was mostly co-expressed with CD68 and CD163 and the cells were negative for CD20.

CONCLUSIONS: The cyclin D1-positive CLL/SLL cells in this study were mostly histiocytes. The expression of cyclin D1 by histiocytes may mimic cyclin D1+ CLL/SLL; thus, the recognition of cyclin D1 expression by non-lymphoid cells in lymphoma is important.