52. A case of ALK-positive large B cell lymphoma

A 63-year-old male presented with cervical lymphadenopathy. Metastatic carcinoma was the favoured diagnosis, and a neck dissection was performed. 23 of 32 nodes showed partial to total replacement by large malignant cells with a plasmablastic appearance. A sinusoidal pattern of invasion was noted. Metastatic melanoma, mesothelioma and germ cell tumour were excluded by negative staining for S100, HMB45, Calretinin, PLAP and OCT3/4. The cells were focally positive for LCA. There was granular cytoplasmic staining for cytokeratin and positive staining for EMA. B cell markers CD20, CD79a and PAX5 were negative. There was positive staining for CD138, CD10, OCT2, IgG and BCL6. Granular cytoplasmic staining for ALK protein was present. Staining for CD30 was negative, as was staining for T cell markers CD2, CD3, CD4 and CD5. HHV8 and EBER ISH were negative. FISH using the ALK break apart probe was positive, confirming the presence of an alteration of the ALK locus. The morphologic, immunophenotypic and genotypic features were consistent with ALK-positive large B cell lymphoma. ALK-positive large B cell lymphoma is a rare entity, first described in 1997, with no more than 40 reported cases to date. 1 The pathological findings and differential diagnosis of this uncommon lymphoma are discussed.