[Clinicopathological features of intravascular large B-cell lymphoma and collision tumors of five cases].

Objective: To investigate the clinicopathological characteristics, diagnosis and differential diagnosis of intravascular large B-cell lymphoma (IVLBCL) and its collision tumors. Methods: Five cases of IVLBCL were collected, including 2 cases of collision tumors, and 1 case complicated with liver cirrhosis. The morphology and immunophenotype were analyzed. The related literature was reviewed. Results: There were 2 females and 3 males, aged from 53 to 73 years, with a median age of 65 years. The tumors were located in the lower extremities, right cerebellar hemisphere, left kidney, bilateral nasal cavity, and liver, respectively. Cases 2 and 3 were incidentally found in meningioma and renal cell carcinoma tissues, respectively. Case 5 had a background of liver cirrhosis. Morphologically, atypical large lymphoid cells were located in small blood vessels and capillary lumen, with little cytoplasm, hyperchromasia, prominent nucleoli, and obvious mitotic figures. Immunohistochemically, the IVLBCL tumor cells expressed CD20 and PAX5; 2 cases were CD5 positive. One of the 5 cases was GCB phenotype, and 4 cases were non-GCB phenotype. All cases expressed C-MYC (positive rate was 10%-40%). PD-L1 was positive in 4 cases (positive rate was 60%-90%). Ki-67 proliferation index was 70%-90%. CKpan, CD3, TDT, and CD34 were negative. In case 2, meningioma cells were positive for PR, EMA, and vimentin, but negative for CKpan and PD-L1. In case 3, renal carcinoma cells were positive for CKpan, PAX8, EMA, vimentin, CAⅨ and CD10, while PD-L1 was negative. No EBER expression (by in situ hybridization) or C-MYC gene translocation (FISH, break-apart probe) was detected in any of the 5 cases. Three patients were followed up, and all died within 1-13 months. Conclusions: IVLBCL is a highly aggressive lymphoma, with occult clinical manifestations and poor prognosis. Collision tumors of IVLBCL are extremely rare. A better understanding of IVLBCL would help pathologists avoid misdiagnoses.