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The diagnosis of lymphoplasmacytic lymphoma is often challenging, especially in extramedullary tissues where the differential diagnosis includes nodal marginal zone lymphoma, splenic marginal zone lymphoma, or other small B-cell neoplasms with plasmacytic differentiation. The MYD88 L265P mutation has been recently identified in 490% of bone-marrow-based lymphoplasmacytic lymphoma, but the incidence of this abnormality and corresponding morphologic correlates in nodal lymphoplasmacytic lymphoma have not been established. We analyzed 87 cases of extramedullary lymphoplasmacytic lymphoma, splenic marginal zone lymphoma, unclassifiable splenic B-cell lymphomas, nodal marginal zone lymphoma with plasmacytic differentiation, and chronic lymphocytic leukemia/small lymphocytic lymphoma with plasmacytic differentiation for MYD88 L265P. Eighteen cases (21%) were positive, including 9/9 (100%) lymphoplasmacytic lymphomas with classic histologic features, 5/12 (42%) cases that met 2008 WHO criteria for lymphoplasmacytic lymphoma but with atypical morphologic features, 3/15 (20%) cases initially considered nodal marginal zone lymphoma with plasmacytic differentiation, and 1/6 (17%) unclassifiable splenic B-cell lymphomas. The presence of MYD88 L265P was associated with IgM paraprotein (Po0.001) and a trend for bone marrow involvement (P ¼ 0.09). Each of 44 splenectomy-defined splenic marginal zone lymphomas (19 with plasmacytic differentiation) and the chronic lymphocytic leukemia/small lymphocytic lymphoma with plasmacytic differentiation were negative for the mutation. Morphologic re-review with knowledge of MYD88 mutation status and all available clinical features suggested all MYD88 mutated cases were consistent with lymphoplasmacytic lymphoma (either classic or variant histology), except for one case which remained most consistent with nodal marginal zone lymphoma with plasmacytic differentiation. These results demonstrate the importance of MYD88 mutational analysis in better defining lymphoplasmacytic lymphoma as a relatively monomorphic small B-cell lymphoma with plasmacytic differentiation that may show total nodal architectural effacement and follicular colonization. Cases previously considered lymphoplasmacytic lymphoma that are more polymorphous and are often associated with histiocytes should no longer be included in the lymphoplasmacytic lymphoma category. Clinicopathologic review suggests that although MYD88 mutated non-lymphoplasmacytic lymphoma small B-cell neoplasms exist, they are very uncommon.

BACKGROUND: BRAF mutation V600E (substitution Val600Glu) is a molecular signature for papillary thyroid carcinoma (PTC). Testing for BRAF mutation is clinically useful in providing prognostic prediction and facilitating accurate diagnosis of PTC in thyroid fine-needle aspirate (FNA) samples. METHODS: This study assessed the correlation of cellularity with DNA yield and compared 2 technical platforms with different sensitivities in detection of BRAF mutation in cytologic specimens. Cellularity was evaluated based on groups of 101 cells on a ThinPrep slide: 11 (1-5 groups), 21 (6-10 groups), 31 (11-20 groups), and 41 (> 20 groups). Genomic DNA was extracted from residual materials of thyroid FNAs after cytologic diagnosis. RESULTS: Approximately 49% of thyroid FNA samples had low cellularity (1-21). DNA yield is proportionate with increased cellularity and increased nearly 4-fold from 11 to 41 cellularity in cytologic samples. When applied to BRAF mutational assay, using a cutoff of 6 groups of follicular cells with 101 cells per group, 96.7% of cases yielded enough DNA for at least one testing for BRAF mutation. Five specimens (11.6%) with lower cellularity did not yield sufficient DNA for duplicate testing. Comparison of Sanger sequencing to allele-specific polymerase chain reaction methods shows the latter confers better sensitivity in detection of BRAF mutation, especially in limited cytologic specimens with a lower percentage of malignant cells. CONCLUSIONS: This study demonstrates that by using 6 groups of 101 follicular cells as a cutoff, nearly 97% of thyroid FNA samples contain enough DNA for BRAF mutational assay. Careful selection of a molecular testing system with high sensitivity facilitates the successful conduction of molecular testing in limited cytologic specimens.

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