1461P - Predictive value of residual FDG-PET metabolic activity in metastatic non-small cell lung cancer (mNSCLC) patients (pts) with long-lasting response to immune checkpoint inhibitors (ICIs)

Background

The optimal duration of ICIs treatment in mNSCLC is debated, arbitrarily fixed to 2 years in the 1st line setting. Unfortunately, pts will mostly relapse months or years after the end of the treatment (EOT). Physicians tend to confirm the partial or complete obtained response before stopping it, by performing ¹⁸F-FDG -PET (PET). However, the interpretation of residual fixative areas remains unclear.

Methods

This is a bi-center retrospective study of mNCSLC pts who completed 2 years of ICI, or stopped it due to adverse event without progression and underwent a PET at the EOT. Collected data were: age, smoking status, PDL1 and KRAS status, type and line of treatment, ICI duration.

Results

We enrolled 80 pts who began ICIs between Sept. 2016 and Nov. 2021. Median follow up was 35.9 months. Median age was 61 years (range: 56-69), sex ratio was 1:1, 93.5% were current/former smokers, 87.5% had adenocarcinoma, 54% had PDL1>50%. ICI was given as monotherapy and as first line in 41% and 67.5% of pts respectively. Molecular analysis revealed KRAS G12C mutation in 29% pts. Median ICIs duration was 23.4 months (range: 3-48), 55 pts completed 2 years of ICI, 22 discontinued due to toxicity, 3 for others reasons. The 2-year progression-free survival (PFS) probability was 96% (range:92-100). Median SUVmax was 1.9 (range: 0-17). 55% pts had PET residual fixation (RF): 36% on initial lung tumor, 15% on mediastinal lymph nodes and 5% on extrathoracic sites. 6 pts underwent an excision surgery or a biopsy of a RF: 4 were immune-mediated inflammatory reactions, 2 found the initial histology. 6 pts were locally treated for RF by radiotherapy or surgery. Of the 17 pts who relapsed: 12 had a RF on the PET after ICIs. Conversely, 5/36 pts (14%) without RF relapsed. The presence of a RF was not associated with the PFS in univariable analysis (HR=2.4, 95%CI: 0.8-6.9, P=.121) and after adjusting for duration and type of ICI treatment (HR=1.4, 95%CI: 0.5-4.3, P=.539).

Conclusions

Positive 18F-FDG-PET/CT is not associated with relapse after completion of ICI treatment but has good negative predictive value. Treatment of oligopersistence after partial response to ICI based on PET-scan remains controversial.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Sophie Cousin.

Funding

Has not received any funding.

Disclosure

C. Domblides: Financial Interests, Personal, Advisory Board: AstraZeneca, BMS, MSD; Financial Interests, Personal, Other, travel expenses: AstraZeneca, BMS, MSD. All other authors have declared no conflicts of interest.