A 29-year-old, previously healthy man has had an enlarging nodular area on his arm for the past 8 months. On physical examination, there is an ulcerated, reddish violet, 3x7 cm lesion on his right forearm and nontender right axillary and left inguinal lymphadenopathy. A chest radiograph shows a 4-cm nodular left pleural mass. An abdominal CT scan shows a 5-cm right retroperitoneal mass. Biopsy of an inguinal node is performed, and microscopic examination shows large cells, some of which contain horseshoe-shaped nuclei and voluminous cytoplasm. The tumor cells cluster around venules and infiltrate sinuses. The patient goes into remission after chemotherapy. Which of the following markers is most likely to be positive in the tumor cells?
High-Yield Explanation
This patient has a form of T-cell neoplasm known as anaplastic large-cell lymphoma, which most often appears in children and young adults. It is often extranodal and has a characteristic gene rearrangement on chromosome 2p23 that results in production of anaplastic lymphoma kinase (ALK) with tyrosine kinase activity. CD10 is a B-cell marker. The T-cell proliferations involving skin, known as mycosis fungoides/ Sezary syndrome, are CD4+. The c-KIT proto-oncogene has been associated with some NK cell lymphomas. The IL-2 receptor is associated with lymphohistiocytosis with macrophage activation. The p24 antigen is part of HIV, which is most often associated with B-cell neoplasms.