In Stage I-II primary mediastinal B-cell lymphoma (PMBL), bulky or non-bulky, is post-chemotherapy radiotherapy still standard in patients with a complete response to CHOP-R chemotherapy?

Primary mediastinal B-cell lymphoma (PMBCL) is a rare subtype of DLBCL. It is a clinicopathologic entity by WHO criteria (which makes it occasionally difficult to conclusively diagnose). The typical patient is young, female, with a large, anterior mediastinal mass. The optimal therapy for PMBCL is controversial, both in terms of choice of chemotherapy and whether RT should be utilized afterward. Some centers advocate more intense regimens such as MACOP-B or dose adjusted EPOCH-R. A single institution prospective study showed the latter was associated with excellent outcomes without RT (NEJM 2013;368:1408). Other centers prefer standard R-CHOP. Most patients have a residual mediastinal mass after treatment and PET imaging is invaluable in assessing response to chemotherapy.

I generally recommend consolidation RT after R-CHOP even when a complete response is achieved by PET (30 Gy). A negative PET does not mean all cancer has been eradicated, simply that a good response to chemotherapy has been achieved. With more intense regimens, such as DA-EPOCH-R, where relapse rates appear to be < 10%, the incremental benefit of consolidation RT may be small. A randomized trial, though appealing, would be difficult to perform due to the small number of eligible patients.