If there was overlap in immunohistopathologic features, which test was used to confirm the diagnosis?

• A. PARR
• B. Flow cytometry
• C. ELISA
• D. Western blot

Answer: (A)

When immunohistochemical features collide and can’t clearly distinguish neoplastic from reactive lymphoid tissue, testing for clonality helps seal the diagnosis. PARR checks for clonal rearrangements in antigen receptor genes (immunoglobulin genes for B cells, T-cell receptor genes for T cells) using PCR. A single dominant clone supports lymphoma, while a polyclonal pattern points to a reactive process. This makes PARR the preferred confirmatory test when IHC/ morphology are overlapping. Other options don’t assess clonality: ELISA and Western blot detect proteins, and flow cytometry, while useful for immunophenotyping, may not resolve ambiguity in cases with overlapping features or fixed tissue where clonality is uncertain.