An unusual case of cutaneous Waldenström macroglobulinemia with the MYD88 L265P mutation.

Waldenström macroglobulinemia is a lymphoplasmacytic lymphoma with bone marrow involvement and a monoclonal IgM gammopathy. Infiltration of the skin by neoplastic cells is very rare, and it can be difficult to distinguish from marginal zone lymphoma. The MYD88 L265P mutation is strongly associated with Waldenström macroglobulinemia, and it may be helpful in differentiating the two disorders, although the presence of this mutation is not specific, and other factors must be considered when making the final diagnosis. We present a diagnostically challenging case of cutaneous Waldenström macroglobulinemia in which the MYD88 L265P mutation was identified in the skin but not in the bone marrow, due to a low tumor burden.