PET Plus CT-Assessed Relative Tumor Size Reduction After Chemotherapy Identifies High Risk for Progression and Relapse in Advanced Hodgkin Lymphoma


Key Points

  • Patients with PET-positive residual disease after chemotherapy and poor tumor shrinkage measured by CT are at high risk of progression or relapse.
  • Risk assessment after chemotherapy on the basis of CT alone has little predictive value.

Positive positron-emission tomography (PET) scans have low positive predictive value after chemotherapy in patients with Hodgkin lymphoma. In a study reported in the Journal of Clinical Oncology, Kobe et al assessed whether use of pretreatment and post-treatment computed tomography (CT) could improve outcome prediction. They found that the combination of PET and relative tumor size reduction as determined by CT identifies patients at high risk for progression and early relapse.

Study Details

The study involved 739 patients with residual disease ≥ 2.5 cm after chemotherapy from a total of 2,126 patients in the German Hodgkin Study Group HD15 trial. Patients achieving partial remission after chemotherapy with at least one involved nodal site of ≥ 2.5 cm in the maximal long axis diameter as measured in the transversal or coronal plane by CT underwent PET scanning.

Local radiotherapy (30 Gy) was restricted to patients with partial remission, residual disease ≥ 2.5 cm, and a PET scan that was rated as positive by a central review panel. The panel performed image analysis and interpretation of CT scans before and after chemotherapy and PET scans after chemotherapy. Prognosis was evaluated using progression-free survival.


Among all patients, 548 (74%) patients had PET-negative residues after chemotherapy. These patients did not receive additional radiotherapy and had 4-year progression-free survival of 91.5%. The remaining 191 PET-positive patients (26%) received additional radiotherapy and had 4-year progression-free survival of 86.1% (P = .022).

The CT-based separation of patients into groups with higher and lower risks of progression independent of PET results failed to identify patients with higher or lower risk for progression or relapse. On the basis of PET, 19% of 575 patients in the CT low-risk group and 44% of 164 in the CT high-risk group received radiation therapy. There was no separation between high-risk and low-risk patients according to CT alone in the PET-positive (P = .7) and PET-negative subgroups (P = .9).

High-Risk Group

In the 54 PET-positive patients with a relative tumor reduction of < 40%, 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% confidence interval = 5.8%–30%).

The investigators concluded, “To improve on the predictive value of a positive PET scan, we used the degree of tumor reduction during chemotherapy in patients who were PET-positive to better define possible risk groups for treatment failure. We found that the combination of PET and relative tumor size reduction as determined by CT can identify patients at high risk for progression and early relapse. We further demonstrated that the risk evaluation after chemotherapy as determined by CT alone has little predictive value.”

Carsten Kobe, MD, of University Hospital of Cologne, is the corresponding author for the Journal of Clinical Oncology article.

The study was supported by Deutsche Krebshilfe. The study authors reported no potential conflicts of interest.

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