Abstract
The genetic complexity of multiple myeloma is due in part to the accumulation of mutations, with primary and secondary events. One such secondary event is the development of a gene mutation that may result in overexpression of cyclin D1. The pathway involving cyclin D1 is intricately involved in cell cycle regulation from the G1 to S phase, and alterations may contribute to tumorigenesis. We present a case of cyclin D1–positive multiple myeloma with lymphoplasmacytic morphology and discuss potential diagnostic pitfalls and effects on prognosis.