Anaplastic lymphoma kinase positive large b-cell lymphoma mimicking metastatic carcinoma of the cervical lymph node from an unknown primary lesion

Anaplastic lymphoma kinase positive large B-cell lymphoma (ALK+LBCL) is a rare subtype of B-cell lymphoma with aggressive features and a poor prognosis. The rarity of this disease and similarity of microscopic features with undifferentiated epithelial neoplasm disturb the provision of proper treatment. A 57-year-old male presented with a rapidly growing and painless mass on the left side of the neck. Metastatic carcinoma of an unknown primary (CUP) lesion was initially suspected based on the pathologic results obtained from a core needle biopsy, but it was finally diagnosed as ALK+LBCL after a modified radical neck dissection. We herein report a case of ALK+LBCL mimicking CUP with a literature review.