Assessment of Tumor Size Reduction Improves Outcome Prediction of Positron Emission Tomography/Computed Tomography After Chemotherapy in Advanced-Stage Hodgkin Lymphoma

Purpose Positron emission tomography (PET) after chemotherapy can guide consolidating radiotherapy in advanced-stage Hodgkin lymphoma (HL). This analysis aims to improve outcome prediction by integrating additional criteria derived by computed tomography (CT). Patients and Methods The analysis set consisted of 739 patients with residues ≥ 2.5 cm after chemotherapy from a total of 2,126 patients treated in the HD15 trial (HD15 for advanced stage Hodgkin's disease: Quality assurance protocol for reduction of toxicity and the prognostic relevance of fluorodeoxyglucose-positron-emission tomography [FDG-PET] in the first-line treatment of advanced-stage Hodgkin's disease) performed by the German Hodgkin Study Group. A central panel performed image analysis and interpretation of CT scans before and after chemotherapy as well as PET scans after chemotherapy. Prognosis was evaluated by using progression-free survival (PFS); groups were compared with the log-rank test. Potential prognostic factors were investigated by using receiver operating characteristic analysis and logistic regression. Results In all, 548 (74%) of 739 patients had PET-negative residues after chemotherapy; these patients did not receive additional radiotherapy and showed a 4-year PFS of 91.5%. The 191 PET-positive patients (26%) receiving additional radiotherapy had a 4-year PFS of 86.1% (P = .022). CT alone did not allow further separation of patients in partial remission by risk of recurrence (P = .9). In the subgroup of the 54 PET-positive patients with a relative reduction of less than 40%, the risk of progression or relapse within the first year was 23.1% compared with 5.3% for patients with a larger reduction (difference, 17.9%; 95% CI, 5.8% to 30%). Conclusion Patients with HL who have PET-positive residual disease after chemotherapy and poor tumor shrinkage are at high risk of progression or relapse.