CYTOKERATIN-POSITIVE LARGE-CELL LYMPHOMAS OF B-CELL LINEAGE - A STUDYOF 5 PHENOTYPICALLY UNUSUAL CASES VERIFIED BY POLYMERASE CHAIN-REACTION

Five cases of clinically aggressive, keratin-positive malignant lympho mas of B-cell type with unusual immunophenotypes were studied. All cas es were extranodal: two from the stomach, one from soft tissue, one fr om the skin, and one from the spleen. These tumors were undifferentiat ed large-cell neoplasms that showed reactivity for low-molecular-weigh t keratin 8, but they were negative for keratin 19; three cases were a lso positive for epithelial membrane antigen. The immunohistochemical diagnosis was complicated by the fact that two of these cases lacked r eactivity for leukocyte common antigen and three were CD20 negative. T hese findings simulated the immunophenotype of a carcinoma and led to an initial misdiagnosis of carcinoma. Although only two cases showed i mmunohistochemical evidence of B-cell lineage (CD20 +), all five cases were documented as B-cell lymphomas on the basis of the clonal immuno globulin heavy-chain gene rearrangement, as demonstrated by polymerase chain reaction (PCR) in all the cases and by Southern blot hybridizat ion in three cases; all cases were negative for T-cell markers, and th ree cases showed germline configuration for T-cell receptor beta-chain . One case was strongly CD30 positive and represented large-cell anapl astic lymphoma of B-cell type. Our results show that some B-cell lymph omas can have unusual and confusing immunophenotypes, including kerati n positivity and leukocyte antigen negativity. Use of PCR-based molecu lar genetic demonstration of clonal immunoglobulin heavy-chain gene re arrangement is helpful in establishing the correct diagnosis in such c ases.