## Pathognomonic Cell of Classical Hodgkin Lymphoma **Key Point:** Reed-Sternberg (RS) cells are the diagnostic hallmark of classical Hodgkin lymphoma (cHL). They are large, multinucleated or multilobated cells with prominent eosinophilic nucleoli ("owl's eye" appearance). ### Morphologic Features of RS Cells | Feature | Description | | --- | --- | | **Size** | 20–50 μm or larger | | **Nuclei** | Multiple (≥2), often 10+ | | **Nucleoli** | Prominent, eosinophilic, resembling owl's eyes | | **Cytoplasm** | Abundant, basophilic | | **Membrane** | Thick, well-defined | ### Related Cell Types - **Hodgkin cells:** Mononuclear variants of RS cells; also diagnostic but less specific. - **Lacunar cells:** RS cells in formalin-fixed tissue that appear to sit in empty spaces ("lacunae") due to retraction artifact. - **Mummified cells:** Apoptotic/degenerating RS cells; not diagnostic on their own. **High-Yield:** RS cells are CD30^+^, CD15^+^, and typically CD45^−^, CD20^−^ (weak or absent), and EBV^+^ (in some cases, especially mixed cellularity subtype). **Clinical Pearl:** The presence of even a few RS cells in a background of small lymphocytes, eosinophils, and histiocytes is sufficient for diagnosis of cHL, provided the morphology and immunophenotype are consistent.
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