Abstract
Background : ALK-positive anaplastic large cell lymphoma (ALK+ALCL) mostly occurs in patients under 40 years of age, and often involves both lymph nodes and extranodal sites, including soft tissues. In those cases where it forms a large soft tissue mass, it suggests a soft tissue tumor of various differential diagnoses, including small round cell tumors, sarcomas or metastatic tumors.
Case : A female patient in her middle thirties was admitted with the chief complaint of hip pain. Magnetic resonance images revealed an irregular mass more than 6.5 cm in diameter in the left retroperitoneum. At needle biopsy, cells were collected from the needle by washing. On the cell smears, there were numerous roundish or polygonal atypical cells. Some cells were small and showed a high N/C ratio, and others had abundant clear cytoplasm and horseshoe-like or kidney-shaped nuclei, which were the so-called “hallmark cells” of ALK+ALCL. Small epithelioid clusters or paired cells were also found. Such cytologic features were almost concordant with the histologic features of biopsy specimens. Immunohistochemistry confirmed that the tumor cells were diffusely positive for CD30 and ALK.
Conclusion : Cytology is helpful in the diagnosis of ALK+ALCL that involves deep soft tissues.
