B‐cell lymphoma, Unclassifiable with features intermediate between diffuse large B‐cell lymphoma (DLBCL) and Burkitt lymphoma, for convenience referred to here as unclassifiable B‐cell lymphoma, is a category in the 2008 World Health Organization system used for a group of histologically aggressive neoplasms that are difficult to classify definitively. Currently, there is no established standard therapy for these neoplasms.

The authors assessed MYC status and correlated it with treatment response and outcome in a group of 52 patients with unclassifiable B‐cell lymphoma treated with either a standard DLBCL regimen (R‐CHOP [rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisolone‐related therapy]) or more intensive regimens, such as R‐hyper‐CVAD (rituximab plus hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone alternating with high‐dose methotrexate and cytarabine). The regimens were selected by the treating clinicians based on the overall clinical and pathological findings.

Thirty (58%) unclassifiable B‐cell lymphomas had MYC abnormalities (MYC⁺) including 27 with rearrangement, 2 with amplification, and 1 with both. The MYC⁺ and MYC⁻ groups were similar in their age distribution and International Prognostic Index scores. Progression‐free survival of patients with MYC⁺ unclassifiable B‐cell lymphoma treated initially with R‐CHOP was significantly worse than patients treated with R‐hyper‐CVAD (P = .0358). In contrast, for the MYC⁻ unclassifiable B‐cell lymphoma group, some patients responded to R‐CHOP, and others were refractory to R‐hyper‐CVAD.

MYC aberrations are common in unclassifiable B‐cell lymphoma. The presence of MYC aberrations identifies a patient subset that requires more aggressive therapy than R‐CHOP. In contrast, MYC⁻ unclassifiable B‐cell lymphoma patients responded variably to either R‐CHOP or aggressive therapy, and the latter showed no survival advantage. Cancer 2011;. © 2011 American Cancer Society.