Interim FDG PET Imaging in CALGB 50203 Trial of Stage I/II Non-Bulky Hodgkin Lymphoma: Would Using Combined PET and CT Criteria Better Predict Response Than Each Test Alone?,

Abstract 3644 Use of interim PET in Hodgkin Lymphoma (HL) for risk-adapted treatment has been confounded by a lack of standardized criteria for interpretation. The International Harmonisation Project (IHP) criteria (JCO 2007;25:571) have been validated and are widely used for restaging following therapy. Our objective was to validate the IHP criteria for response evaluation based on PET after two cycles and correlate with the “London”criteria and diagnostic CT-based (dCT) lesion size changes. Methods: Pts were accrued prospectively to CALGB 50203, a trial of doxorubicin, vinblastine and gemcitabine (AVG) for initial treatment of stage I-II non-bulky Hodgkin lymphoma (HL). All had FDG PET or PET/CT and a separate high-resolution dCT scan at baseline, after two cycles of AVG (PET-2 and dCT-2) and at the end of therapy. No treatment change was made based on the PET-2 results. Of 99 assessable pts, 88 had both PET-2 and dCT-2. The primary PET-2 interpretation was based on IHP criteria (uptake > mediastinal blood pool/background is positive), a secondary interpretation was performed using the 5 point London criteria (uptake > liver is positive). The percent decrease in the sum of the products of the diameter (%SPPD) was determined between baseline dCT and dCT-2. A receiver operator curve (ROC) analysis was performed to determine the best cut-off for %SPPD to define a positive and negative CT result. The PET-2 and dCT-2 (%SPPD change) data were correlated with progression free survival (PFS). Results: Sixty-four pts (73%) achieved a complete remission (CR)/CR unconfirmed (CRu), 23.9% a partial response (PR), and 3% had stable disease. After a median follow-up of 3.3 years (1.8–5.0 years), 23.9% of patients relapsed/progressed with an estimated 3-year PFS of 0.77 [CI 68,84]. Eleven of 24 (45.8%) PET-2 positive patients relapsed vs. 10 of 64 (15.6%) PET-2 negative patients (p=0.0004). The best cut-off determined from ROC analysis for %SPPD change was 65%. The comparative results for individual evaluation criteria are displayed in the Table. In the PET-2 positive group, a negative dCT-2 increased PFS by 27–35%, suggesting an influence from dCT-2 results. However, in the combinatorial analysis, some of the confidence intervals are large due to small number of patients in each individual group, particularly, when both PET-2 and dCT-2 were positive as well as when PET-2 was positive and dCT-2 was negative. Conclusions: Interim PET/CT after two cycles of chemotherapy using either IHP or London criteria has a high NPV in early stage non-bulky HL. However, the PPV of interim PET needs to be improved to guide clinical management. Combining PET-2 with %SPPD decrease after 2 cycles improves prediction of PFS compared to each test alone . These data provide a proof of concept for risk-adapted clinical trials and further studies are underway to confirm these findings in a larger population. Disclosures: Bartlett: seattle genetics: Research Funding. Cheson: Celphalon: Membership on an entity9s Board of Directors or advisory committees, Research Funding; Celegen: Membership on an entity9s Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Research Funding.