Our patient had very non-specific symptoms and signs at the start, but as these persisted an X ray was performed which showed a mediastinal mass. Differential diagnoses included thymoma, non-Hodgkin’s lymphoma, Hodgkin’s lymphoma, teratoma, benign tumour. A concern was superior vena caval obstruction so further investigations were performed urgently. CT confirmed an anterior mediastinal mass and demonstrated some compression of the SVC. A tissue biopsy was performed and steroids were started pending the results. We wanted to avoid the use of steroids if at all possible prior to biopsy as this may shrink the tumour, rendering the interpretation difficult. The histology confirmed primary mediastinal B cell lymphoma.
Primary mediastinal B cell lymphoma
This is a rare subtype of non-Hodgkin’s lymphoma. Comprising approximately 2% NHL and 5% diffuse large B cell lymphoma. It is classified as a type of DLBCL but shares certain genetic abnormalities which make it similar to Hodgkin’s lymphoma. It is thymic in origin. It is often bulky at presentation and can cause pleural and pericardial effusion as well as SVCO. It is more unusual for it to be extranodal. Mutations in the B cell lymphoma 6 gene are common. It commonly presents in the second, third and fourth decade and is more common in women.
The outlook for patients with PMBCL is good, with most patients achieving a complete and lasting remission. However for those that don’t achieve complete remission, the outlook is very poor. Because of the rarity of PMBCL treatment is non-standardised and good quality trials are difficult to perform. A number of regimes are available:
- R-CHOP (Rituximab, cyclophosphamide, doxorubicin, vincristine, prednisolone)
- R-MACOP-B (Rituximab/methotrexate/doxorubicin/cyclophosphamide/vincristine/ prednisone/bleomycin)
- DA-EPOCH-R ( dose adjusted: etoposide, prednisolone, vincristine, cyclophosphamide, doxorubicin, rituximab)
These regimes are combination chemotherapy and rituximab regimes. There has been no randomised controlled trials into these different regimes. Sometimes groups will combine with consolidation radiotherapy and/or autologous haematopoietic stem cell transplantation. A recent trial advocates the use of DA-EPOCH-R without radiotherapy. Where possible patients showed be entered into clinical trials. The treatment of relapsed disease is suboptimal. PET scans may help to see who should receive further consolidation therapy.