Utility of ultrasensitive, US Food and Drug Administration–approved κ and λ dual in situ hybridization assay in the diagnosis of Hodgkin lymphomas

Objectives Determination of B-cell clonality in formalin-fixed, paraffin-embedded tissues is challenging, especially in cases where tumor B cells are sparse. Flow cytometry is of limited utility in Hodgkin lymphomas, at least in part due to the rarity and fragility of the malignant cells. Methods We used a recently US Food and Drug Administration–approved, ultrasensitive κ and λ dual in situ hybridization assay (K/L dual ISH; Roche/Ventana Medical Systems) to evaluate B-cell clonality in 184 classic Hodgkin lymphomas (CHLs) and 113 nodular lymphocyte-predominant Hodgkin lymphomas (NLPHLs). Results Five CHLs and 11 NLPHLs were not scorable due to preanalytical variables. Of the 179 scorable CHL cases, none showed light chain messenger RNA expression in the Hodgkin/Reed-Sternberg cells, whereas 89% of NLPHLs (91/102) exhibited light chain expression in lymphocyte-predominant (LP) cells. Among NLPHLs, 66% (68/102) showed κ restriction, 20% (21/102) showed λ restriction, and 1.9% (2/102) showed dual κ and λ expression in the LP cells. There was no appreciable light chain expression in 10% (11/102) of cases. Conclusions Although morphology and immunohistochemistry are usually sufficient to separate CHL from NLPHL, determining light chain restriction by K/L dual ISH could provide a valuable adjunct in challenging cases, potentially improving diagnostic accuracy and patient outcomes.