Response criteria for NHL: Importance of 'normal' lymph node size and correlations with response rates

Background: Oncologic literature cites many different definitions of critical response measurements. Patients and methods: Response criteria (RC) for non-Hodgkin's lymphoma (NHL) were developed by lymphoma experts, endorsed by international lymphoma clinicians, and applied to a 166-patient rituximab (Rituxan®, MabThera®) trial by a third-party, blinded panel of NHL experts (LEXCOR). Retrospectively, we analyzed this data using variations of the original RC and comparing with recently published RC. Results: The definition of a 'normal' lymph node affected the complete response (CR) rate (≤1.0 x 1.0 cm, 6%; ≤1.5 x 1.5 cm, 18%; ≤2.0 x 2.0 cm, 28%); overall response rate (ORR) was not affected. CR rates increased progressively without ≥28 days response confirmation: 12% vs. 6% (≤1.0 x 1.0 cm), 26% vs. 18% (≤ 1.5 x 1.5 cm), and 36% vs. 28% (≤ 2.0 x 2.0 cm). CR rate and duration of response (DR) were unaffected when only the six largest, rather than all lesions, were measured. When the new RC were applied, CR rate (32%) was higher and DR (13.9 months) and time to progression (15.6 months) were shorter in complete responders. Conclusions: Standard RC must be consistently and rigorously applied for accurate comparisons between studies.