F-18 FDG PET/CT evaluation of treatment response to ipilimumab therapy in advanced stage melanoma

Objectives Ipilimumab is a recently approved agent for treatment of melanoma, which is reported to improve the survival in advanced stage disease. F-18 FDG PET/CT has been widely used in staging, prognosis, and follow-up of melanoma. This study used the PERCIST criteria to investigate the predictive value of F-18 FDG PET/CT exam in advanced stage melanoma treated with ipilimumab.

Methods This was a retrospective, IRB-approved study. 93 patients with Stages III and IV unresectable melanoma were treated with ipilimumab from 2011 to 2014. Data from 28 cases (mean age=66 ±13 years, female n=11) with complete follow-up and FDG PET/CT before and after 2-4 cycles of treatment were analyzed. Treatment responses were assessed according to PERCIST criteria by measuring the post-treatment changes of SUVmax compared with clinical outcome.

Results Clinical disease progression (PD) was present in 21 out of 28 patients (pts). Post therapy PET/CT showed progressive metabolic disease (PMD) in 14 pts, partial metabolic response (PMR) in 7 pts, stable metabolic disease (SMD) in 5 pts, and complete metabolic response (CMR) in 2 pts. PMD was highly correlated with clinical PD (Positive Predictive Value [PPV]=93%, 13/14), and PMD pts showed worse long-term survival than the non-PMD pts (p=0.046 in log-rank test). One year survival rates for PMD and non-PMD were 58% and 100%, and two year survival rates were 31% and 73%, respectively. Patients of non-PMD after ipilimumab therapy demonstrated progression-free survival rates of 62% and 31% at one and two years respectively.

Conclusions PET/CT evaluation using the PERCIST criteria at the end of ipilimumab therapy can be used to predict the survival for melanoma patients, with a high PPV when PMD was found. PMD after 2-4 cycles of ipilimumab predicts poor survival.