Abstract LBA021: Immune resistance interrogation study (IRIS): Initial report of next generation sequencing (NGS) results in patients with primary versus acquired resistance to anti-PD1/L1 antibodies
Authors: Genta Sofia , Aghababazadeh Farnoosh Abbas , Tsao Ming S , Hansen Aaron R , Butler Marcus O , Razak Albiruni R , Bedard Philippe L , Wang Ben X , Trevor Pugh J , Hakgor Sevan , Woo Jeffrey , Haibe-Kains Benjamin , Siu Lillian L , Spreafico Anna 
Published: December 2021

Background: The molecular mechanisms underlying primary versus acquired resistance to anti-PD-1/L1 antibodies have not been comprehensively evaluated across different tumor types. Methods: The Immune Resistance Interrogation Study (IRIS; NCT04243720) is a prospective, investigator-initiated study at the Princess Margaret Cancer Centre, aimed to perform extensive multi-omic characterization of solid tumors with primary resistance (disease progression on first imaging; or stable disease &lt;6 months) versus acquired resistance (partial or complete response; or stable disease ≥6 months) to antiPD-1/L1 agents. A one-time fresh tumor biopsy is collected from patients (pts) who have progressed on anti-PD1/L1 antibody-based treatment as their most recent line of therapy; liquid biopsy or archived FFPE tissue is allowed as alternates when fresh biopsy is insufficient. NGS was performed using Foundation One (324 genes) or Foundation Liquid (309 genes) panels. Frequencies of disrupted genes and variants were compared in pts with primary versus acquired resistance using Fisher’s exact test. The planned samples size of IRIS is 100 pts. Results: Among the first 35 pts enrolled, 22 (63%) had primary resistance and 13 (37%) had acquired resistance. The most common diagnosis was melanoma (17 pts; 49%); followed by head and neck squamous cell carcinoma (13 pts; 37%); endometrial cancer (2 pts; 6%); pleural mesothelioma, gastroesophageal junction and colorectal cancer (1 pt each; 3%). Foundation One was performed in 23 pts (66%), 22 of them (63%) had biopsies with sufficient quality for NGS, and 1 (3%) had the analysis performed using archival FFPE tissue. The remaining 12 pts (34%) had Foundation Liquid testing done using liquid biopsy. Thirty-three pts (94%) had at least one oncogenic alteration. Genes most frequently altered included: TP53 in 16 patients (46%), TERT promoter in 12 pts (34%), CDKN2A in 9 pts (26%), PIK3CA in 6 pts (17%), and PTEN in 5 pts (14%). At the variant level, the most frequent alterations were: TERT promoter -146C&gt;T mutation in 6 patients (17%), followed by TERT promoter -124C&gt;T mutation in 5 patients (14%), FGF19/FGF4/FGF3 and CCND1 amplifications in 4 pts each (11%), and MDM2 amplification, CDK4 amplification and CDKN2A loss, detected in 3 pts each (9%). Pts with acquired resistance had a higher frequency of TP53 mutations (9/13 = 69%) compared to primary resistance pts (7/22 = 32%), p=0.04; however this was not significant when corrected for multiple testing. Interestingly, amplifications in CDK4, CCND1, FGF 19/FGF 3/FGF 4, MDM2 and mutations in NF1 were only identified in pts with primary resistant tumors. Conclusions: No significant differences in disrupted genes and variants were observed in the current analysis. However, this can be due to the small number of pts analyzed thus far. Accrual to this study is ongoing. A comparison of alterations in oncogenic pathways is planned to further define the genomic landscape of pts with primary versus acquired resistance to anti-PD1/PDL1 blockade.

Citation Format: Sofia Genta, Farnoosh Abbas Aghababazadeh, Ming S Tsao, Aaron R Hansen, Marcus O Butler, Albiruni R Razak, Philippe L Bedard, Ben X Wang, Pugh J Trevor, Sevan Hakgor, Jeffrey Woo, Benjamin Haibe-Kains, Lillian L Siu, Anna Spreafico. Immune resistance interrogation study (IRIS): Initial report of next generation sequencing (NGS) results in patients with primary versus acquired resistance to anti-PD1/L1 antibodies [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA021.