Response assessment in non-small cell lung cancer immunotherapy: initial experiences in utilizing FDG PET/CT and the PD-1 blocker nivolumab

Most Non-Small-Cell lung cancer (NSCLC) patients need systemic treatment. Immunotherapy is now current standard in first- and second-line treatment. In all pivotal studies, staging was performed using conventional computer tomography (CT) scans. PET/CT-based treatment monitoring is on the contrary recommended in NSCLC guidelines. This investigation aims at describing the benefits, challenges and possible pitfalls of using PET/CT-based monitoring for lung cancer during immunotherapy.

We analyzed 11 NSCLC patients treated with nivolumab at a German tertiary care lung cancer center between 2015 and 2016. All patients received at least two follow-up PET-CTs. Evaluation of response was based on both Response Evaluation Criteria in Solid Tumors (RECIST) and PET Response Criteria in Solid Tumors (PERCIST) criteria.

In 7 out of 11 cases, the RECIST and PERCIST results concurred, but two patients with initial stable disease regarding RECIST were reclassified as progressive metabolic disease based on PERCIST criteria. Additionally we identified one case of pseudoprogression using PERCIST criteria in contrast to stable disease using RECIST criteria and one case showing an early and durable response to nivolumab treatment using RECIST, despite a highly hypermetabolic mediastinal lymph node metastasis.

The findings indicate that the PERCIST-based evaluation could identify progressive disease earlier. Early identification of nonresponders could lead to prevention of overtreatment and to an early switch to a more effective therapy.