Primary mediastinal (thymic) large B-cell lymphoma is a distinct type of diffuse large B-cell lymphoma involving the mediastinum, recognized in the WHO 2008 classification.[1][2]: 370–374
Primary mediastinal (thymic) large B cell lymphoma | |
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Other names | Mediastinal large B cell lymphoma, primary mediastinal large B-cell lymphoma (PMLBCL), mediastinal large B-cell lymphoma |
Specialty | Hematology, oncology |
Superior vena cava syndrome occurs in 30–50%, and pleural or pericardial effusions occur in about one-third.[3]
PMLBCL arises from a putative thymic peripheral B cell.[3][4] It has several distinctive biological features.[3] Molecular analysis shows that PMLBCL is distinct from other types of diffuse large B-cell lymphomas (DLBCL).[4] MAL gene expression is seen in 70%, unlike other diffuse large B-cell lymphomas.[2]: 370 Gene expression profiling shows considerable variance from other DLBCLs and similarity to Hodgkin disease.[5]: 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.[2]: 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.[3] At initial presentation, PMLBCL is usually confined to mediastinum, but its bulk, rather than additional adenopathy, can sometimes be palpated at the low neck.[3] Increased LDH is seen in approximately 75%,[2]: 370 [3] but unlike other large cell lymphomas, no increase in beta-2 microglobulin is seen even when bulky[2]: 370 which may relate to defective major histocompatibility complex expression.[2]: 370
Multiagent chemotherapy is recommended, but the preferred regimen is controversial, as is consolidative radiotherapy.[3][6][7][8]
It affects primarily young adults; the median age is 37 years.[2]: 370 It is more common in females.[3]