Plasmablastic lymphoma phenotype is determined by genetic alterations in MYC and PRDM1.

Plasmablastic lymphoma is an uncommon aggressive non-Hodgkin B-cell lymphoma type defined as a high-grade large B-cell neoplasm with plasma cell phenotype. Genetic alterations in MYC have been found in a proportion (~60%) of plasmablastic lymphoma cases and lead to MYC-protein overexpression. Here, we performed a genetic and expression profile of 36 plasmablastic lymphoma cases and demonstrate that MYC overexpression is not restricted to MYC-translocated (46%) or MYC-amplified cases (11%). Furthermore, we demonstrate that recurrent somatic mutations in PRDM1 are found in 50% of plasmablastic lymphoma cases (8 of 16 cases evaluated). These mutations target critical functional domains (PR motif, proline rich domain, acidic region, and DNA-binding Zn-finger domain) involved in the regulation of different targets such as MYC. Furthermore, these mutations are found frequently in association with MYC translocations (5 out of 9, 56% of cases with MYC translocations were PRDM1-mutated), but not restricted to those cases, and lead to expression of an impaired PRDM1/Blimp1α protein. Our data suggest that PRDM1 mutations in plasmablastic lymphoma do not impair terminal B-cell differentiation, but contribute to the oncogenicity of MYC, usually disregulated by MYC translocation or MYC amplification. In conclusion, aberrant coexpression of MYC and PRDM1/Blimp1α owing to genetic changes is responsible for the phenotype of plasmablastic lymphoma cases.

Incidental and Isolated Follicular Lymphoma In Situ and Mantle Cell Lymphoma In Situ Lack Clinical Significance.

Follicular lymphoma in situ (FLIS) and mantle cell lymphoma in situ (MCLIS) are histopathologic findings of undetermined clinical significance. We studied a series of 341 consecutive lymph node resection specimens from patients diagnosed with colorectal (201 cases) and breast (140 cases) adenocarcinoma between 1998 and 2000. Incidental and isolated FLIS was identified in 11/341 patients (3.23%), whereas incidental and isolated MCLIS was found in 2/341 patients (0.59%). None of these cases developed overt lymphoma. A second series of 17 cases of FLIS (16 cases) and MCLIS (1 case) from consultation files was analyzed. Five cases with incidental and isolated FLIS were identified. None of these cases developed overt lymphoma. Overall, none of the 16 cases with incidental and isolated FLIS in both series developed overt FL after a median follow-up of 54 months (range, 7 to 187 mo). However, 12 of these cases with a clinical suspicion of lymphoproliferative disorder showed the association (in different lymph nodes) or combination (in the same sample) of FLIS or MCLIS with other lymphoid neoplasms (FL, splenic marginal zone lymphoma, nodal marginal zone lymphoma, Hodgkin lymphoma, diffuse large B-cell lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, multiple myeloma). In conclusion, the clinical relevance of FLIS and MCLIS seems to strictly depend on the clinical context. Incidental FLIS or MCLIS seem to have a very low risk for transformation, which recommends careful clinical examination after histopathologic diagnosis and conservative management with follow-up for a limited period of time.