Cytomorphologic features of primary anaplastic large cell lymphoma of the psoas muscle: a case report and literature review.

Ki-1 (CD30) positive anaplastic large cell lymphoma (ALCL) is an uncommon malignancy, which may present with nodal as well as extra-nodal disease. Primary skeletal muscle Ki-1 (CD30) positive ALCL is an even rarer event with few cases reported in the literature and only some with published cytomorphologic features. An 83-year-old woman underwent a fine needle aspiration (FNA) of a psoas muscle mass. Smears demonstrated a predominantly discohesive population of large pleomorphic cells. The nuclei were hypechromatic and lobulated, with often multinucleation. Nucleoli were prominent in a subset of cells. Cytoplasmic vacuolization was also present. No lymphoglandular bodies were identified. A cytodiagnosis of malignant cells favoring metastatic melanoma vs. poorly differentiated carcinoma was rendered. Morphologic and immunohistochemical features later revealed a primary psoas muscle Ki-1 (CD30) positive ALCL with negative staining for anaplastic large cell lymphoma kinase (ALK). Cytologic features of ALCL mimic epithelial neoplasms, sarcomas, melanoma and other lymphomas. Although rare, ALCL should be a diagnostic consideration when discohesive pleomorphic malignant cells are encountered on FNA of a muscle neoplasm.