MYD88 L265P mutation analysis is a useful diagnostic adjunct for lymphoplasmacytic lymphoma with pleural effusion.

Lymphoplasmacytic lymphoma (LPL) is a marrow-based lymphoma, rarely involving extramedullary sites, particularly the pleural cavities. The distinction of lymphomatous pleural effusion (PE) in LPL patients from benign effusion is challenging. We conducted this study to examine whether MYD88 L265P mutation analysis is useful in distinguishing benign from lymphomatous PE in four patients with LPL, in which the initial marrow specimens were all positive for MYD88 mutation. In one case each with plasma cell- or lymphocyte-predominant PE, MYD88 mutation was positive, confirming lymphomatous effusion. The other lymphocyte-predominant PE was negative for MYD88 mutation, but was clonally related to a previous nodal biopsy and this PE was also considered to have LPL involvement. The fourth case developed large B-cell lymphoma in the PE 30 months later. The PE specimen was negative for MYD88 mutation but was clonally related to the diagnostic marrow tissue, indicating large cell transformation. Four cases of small lymphocyte-predominant benign PE from patients without history of lymphoma were examined and were all negative for MYD88 L265P mutation. In conclusion, in this small case series we showed that MYD88 L265P mutation analysis could serve as a useful adjunct in distinguishing benign from lymphomatous PE in patients with LPL.