FDG‐PET/CT after two cycles of R‐CHOP in DLBCL predicts complete remission but has limited value in identifying patients with poor outcome – final result of a UK National Cancer Research Institute prospective study

Summary The UK National Cancer Research Institute initiated a prospective study (UKCRN‐ID 1760) to assess the prognostic value of early fluorodeoxyglucose (FDG)‐positron emission tomography (PET)/computed tomography (CT) in diffuse large B‐cell lymphoma (DLBCL). In total, 189 patients with DLBCL treated with R‐CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone) had baseline and post‐cycle‐2 PET (PET2) within a quality assurance framework. Treatment decisions were based on CT; PET2 was archived for central blinded reporting after treatment completion. The association of PET2 response with end‐of‐treatment CT, progression‐free (PFS) and overall survival (OS) was explored. The end‐of‐treatment complete response rate on CT was 83·9%, 75·0%, 70·5%, 40·4% and 36·4% for Deauville score (DS) 1 ( n = 34), 2 ( n = 39), 3 ( n = 46), 4 ( n = 56) and 5 ( n = 14) ( P < 0·001); and 64·1% and 50·0% for the maximum standardised uptake value (∆SUV max ) of ≥66% ( n = 168) and <66% ( n = 21), respectively ( P = 0·25). After a median 5·4 years of follow‐up, the 5‐year PFS was 69·4%, 72·8%, 76·7%, 71·2% and 47·6% by DS 1–5 ( P = 0·01); and 72·6% and 57·1% by ∆SUV max of ≥66% and <66% ( P = 0·03), respectively. The association with DS remained in multivariable analyses, and was consistent for OS. Early complete metabolic response (DS 1–3) at interim PET/CT after two cycles of R‐CHOP in DLBCL was associated with a higher end‐of‐treatment complete and overall response rate; however, only DS‐5 patients had inferior PFS and OS.