Importantly, due to the high clinical association of this disease with the monoclonal lymphoproliferative process with mostly monoclonal IgM kappa light chain restriction, it seems mandatory to investigate for the presence of lymphoma by asking for a lymphoma immunohistochemistry panel including CD20, CD79a, CD3, CD10, CD5, BCL2, BCL6, cyclin D1, CD23, and immunoglobulins light chains, either by immunohistochemistry or by in situ hybridization, as the first step to determine if it is a monoclonal or a polyclonal process. This evidence concerns the gene CD5 and lymphoma.