Detection of MYD88 L265P mutations in formalin-fixed and decalcified BM biopsies from patients with lymphoplasmacytic lymphoma.

The diagnosis of bone marrow (BM) infiltration by Waldenström macroglobulinemia (WM)/lymphoplasmacytic lymphoma (LPL) poses a diagnostic challenge in hematopathology. No definitive morphology or immunophenotype is able to distinguish between infiltration of paraffin-embedded BM sections by WM/LPL and other indolent lymphomas, in particular those of the splenic marginal zone (SMZL) which may also show plasmacytic maturation. An oncogenic gain-of-function mutation (L265P) in the human MYD88 gene has been found to be present in most cases of WM/LPL, yet is absent in most other cases of B-cell chronic lymphoproliferative disorders (LPD), including SMZL. Here, we compare two newly developed diagnostic protocols for detection of this mutation in paraffin-embedded archival tissues which are particularly applicable to decalcified BM biopsies. Sanger sequencing can easily detect levels of BM infiltration above 15% by WM lymphoplasmacytic cells, while the allele-specific PCR can detect the L265P mutation in BM infiltrations below 1% of lymphoma cells. We show that these methods are easily applicable to archival BM specimens and markedly improve diagnostic accuracy of BM infiltrations by indolent B-cell lymphomas.