BACKGROUND
Current immunohistochemical and in situ hybridization (ISH) assays are generally inconclusive for clonality unless plasmacytic differentiation is present. This study examined a series of cytology specimens and explored the ability of a branched‐chain RNA (bRNA) ISH assay for immunoglobulin κ constant (IGKC) and immunoglobulin λ constant (IGLC) to detect a clonal population of B lymphocytes.
METHODS
Pathology databases were used to identify fine‐needle aspiration biopsies (n = 28) and exfoliative cytology samples (n = 20). Demographic, flow cytometry, and excision biopsy results were recorded. bRNA ISH was performed on the Leica Bond platform with the following probes: IGKC, IGLC, immunoglobulin λ‐like polypeptide 5 (IGLL5), and a housekeeping gene (HKG).
RESULTS
The bRNA ISH assay was validated with 30 surgical biopsies. On bRNA ISH, a clonal B‐cell population (light‐chain ratio > 10:1) was detected in 22 of 28 cases with a final diagnosis of lymphoma. In 2 cases, a κ predominance was present, although the ratio was <10:1. Eleven of the 17 κ‐clonal lymphomas also expressed IGLL5, the latter recognized by the presence of an intranuclear signal. Two B‐cell lymphomas lacked IGKC and IGLC, whereas 2 cases were negative for the HKG. In 12 of the 20 cases with reactive lymphoid tissue, bRNA ISH identified a polyclonal lymphoid population. No light‐chain messenger RNA was detected in 6 cases (typically those associated with very few B cells).
CONCLUSIONS
The automated bRNA ISH platform is a robust technique for detecting a clonal B‐cell population in cytology material. Cancer Cytopathol 2016;124:203–212. © 2015 American Cancer Society.