Cyclin D1 expression, cell proliferation, and clonal persistence characterize primary cutaneous CD4 + small or medium T-cell lymphoproliferative disorder.

PCSM-LPD is a clinically indolent, albeit neoplastic, disease driven by clonal expansion of PD1(+)-cells. We demonstrate Cyclin D1-expression associated with accelerated proliferation as a surprising new biological feature of the disease.