Primary mediastinal B-cell lymphoma, abbreviated PMBL or PMBCL, is a rare type of lymphoma that forms in the mediastinum (the space in between the lungs) and predominantly affects young adults.[1][2][3]
PMLBCL arises from a putative thymic peripheral B cell.[6][7] It has several distinctive biological features.[6] Molecular analysis shows that PMLBCL is distinct from other types of diffuse large B-cell lymphomas (DLBCL).[7]MAL gene expression is seen in 70%, unlike other diffuse large B-cell lymphomas.[8]: 370 Gene expression profiling shows considerable variance from other DLBCLs and similarity to Hodgkin disease.[9]: 290–293
PMLBCL is CD20 positive, expresses pan-B markers including CD79a, and has clonal immunoglobulin gene rearrangements and mRNA but paradoxically does not express cytoplasmic or cell surface immunoglobulin.[8]: 370
Clinically, PMLBCL is unusual in several respects. Despite 80% PMLBCL being stage I or II, the presenting anterior mediastinal mass is often over 10 cm and is locally invasive of lung, chest wall, pleura, and pericardium.[6] At initial presentation, PMLBCL is usually confined to mediastinum, but its bulk, rather than additional adenopathy, can sometimes be palpated at the low neck.[6] Increased LDH is seen in approximately 75%,[8]: 370 [6] but unlike other large cell lymphomas, no increase in beta-2 microglobulin is seen even when bulky[8]: 370 which may relate to defective major histocompatibility complex expression.[8]: 370
Multiagent chemotherapy is recommended, but the preferred regimen is controversial, as is consolidative radiotherapy.[6][11][12][13]
Treatment commonly begins with either R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone) or DA-EPOCH-R (dose-adjusted etoposide, prednisolone, vincristine, cyclophosphamide, doxorubicin, rituximab).[14] Other, more intense, regimens may be more effective.[10]PD-1 and PD-L1 inhibitors can be used.[3]
Radiation therapy may be added, especially if chemotherapy does not seem sufficient on its own.[14] Radiation may cause other health problems later, such as breast cancer, and there is some debate about the best approach to it.[10][3]
FDG-PET scanning is not as useful for predicting treatment success in PMBCL as it is in other lymphomas.[10][3]
Prognosis
Most people with PMBCL are successfully treated and survive for many years. However, if the initial treatment is unsuccessful, or if it returns, the long-term prognosis is worse.[14] Relapses generally appear within 12 to 18 months after the completion of treatment.[10]
Epidemiology
This lymphoma is most commonly seen in women between the age of 20 and 40.[10]