The discovery of key driver mutations in the colony-stimulating-factor-3 receptor (<i>CSF3R</i>) gene resulted in the updated World Health Organization (WHO) diagnostic criteria in 2016. A significant number of CNL cases have been associated with plasma cell dyscrasias, predominantly multiple myeloma (MM) and monoclonal gammopathy of unknown significance (MGUS). The gene discussed is CSF3R; the disease is plasma cell neoplasm.