PET-CT detects response to treatment with ipilimumab and nivolumab in malignant mesothelioma far better than CT

Checkpoint-Inhibition with Ipilimumab and Nivolumab is standard-of-care for first-line treatment of patients with unresectable malignant mesothelioma. However, response assessment by conventional CT using modified RECIST might miss detection of response and result in premature treatment discontinuation. PET-CT based assessment might recognize more patients benefitting from this therapy. A retrospective analysis of patients suffering from unresectable malignant mesothelioma who were treated with first-line nivolumab and ipilimumab was performed. Patients got therapy in the Department of Medical Oncology (at the Evang. Kliniken Essen-Mitte or the University Hospital Essen) and underwent PET-CT. Patients received PET-CT scan at their initial diagnosis to clarify resectability (baseline PET-CT). PET-CT scans were repeated after every 12 weeks of treatment. ORR was calculated by using RECIST v1.1, mRECIST, PERCISTSULpeak and PERCISTMTV were used separately to categorize responders in CT and PET imaging studies. 27 patients (19 male (70.4%) and 8 female patients (29.6%) received a baseline PET-CT and underwent therapy with ipilimumab (1mg/kg, q1, q6w) and nivolumab (360 mg abs., d1+22, q6w). Due to clinical progression and/or adverse events, a follow-up PET-CT was performed only in 18 patients (while 3 patients have recently started therapy). In 2 patients (7.4%), CT scan based response assessment showed progressive disease, However, both patients continued treatment due to metabolic response detected in additional PET-CT follow-up scans. Another patient showed progression after 2 cycles, continued therapy due to clinical benefit and responded well after 4 cycles (pseudo-progression). According to follow-up PET-CT scan, 8 patients responded (42.1%), 7 patients achieved diseases stabilization (36.8%) and 4 patients showed progression (21.1%). Median PFS/OS was 8.5/17.3 months. Detailed response assessment with RECIST v1.1, mRECIST, PERCISTSULpeak and PERCISTMTV will be reported at the meeting. PET-CT scans based response assessment identifies mesothelioma patients responding to ipilimumab and nivolumab better than CT scans.