Abstract 3418: Alterations in PIK3CA/PTEN as resistance mechanisms in lung cancer patients progressing on first-line next generation EGFR/ALK tyrosine kinase inhibitors

Abstract Introduction: Advent of targeted therapies has deeply changed treatment of advanced oncogene-addicted non-small cell lung cancer (NSCLC), but development of resistance remains a main issue. Given the efficacy of next generation tyrosine kinase inhibitors (TKIs) against on-target mutations, their first-line administration could increase the relevance of off-target resistance mechanisms. Activating PIK3CA mutations and PTEN loss have been described as putative off-target resistance mechanisms across generations of EGFR TKIs. The role of these alterations in the development of resistance to ALK TKIs has been less described. MATCH-R trial (NCT02517892) is an ongoing prospective study whose objective is to understand mechanisms of acquired resistance to cancer therapies and develop strategies to overcome it. Materials and methods: We collected clinical and molecular data of patients (pts) with NSCLC enrolled in the molecular target group (MTG) of MATCH-R trial. We identified pts with EGFR mutations or ALK rearrangements who developed PIK3CA/PTEN alterations in tissue biopsy and/or circulating tumor DNA upon progression to first-line osimertinib/alectinib. We established patient-derived cell lines (PDCL) from the identified MATCH-R pts and we engineered commercial cell lines (CCL) harboring EGFR mutation (PC9) or ALK fusion (H3122) to constitutively express PIK3CA mutations and/or to have a permanent loss of PTEN. Cell viability assays and Western blot studies with different EGFR/ALK/PI3K/mTOR inhibitors were performed. Results: Of the 186 pts with advanced NSCLC included in the MTG of MATCH-R, 110 (59.1%) harbored EGFR mutations (EGFR+) and 27 (14.5%) ALK rearrangements (ALK+). Among them, 19 received first-line osimertinib and seven first-line alectinib. Five and two pts developed PIK3CA/PTEN alterations in the EGFR+ and ALK+ groups, respectively. In the EGFR+ group, PIK3CA E545K (n=2), R108H, N345K and R357Q mutations were detected. PTEN mutations (F437fs*5 and Y27C) were concomitant with E545K and R357Q mutations, respectively. In both ALK+ pts, a PIK3CA E545K mutation was identified, together with PTEN exon 5 splicing in one case. We confirmed on CCL that PIK3CA E545K mutation, alone or in combination with PTEN loss, confers resistance to second-/third-generation EGFR/ALK TKIs. PTEN loss alone had a moderate impact on TKIs sensitivity. Overcoming strategies combining EGFR/ALK TKIs with PIK3CA/mTOR inhibitors are being evaluated and will be disclosed at the meeting. Conclusions: Activating PI3KCA mutations and molecular events leading to PTEN loss are frequent events at resistance to first-line EGFR/ALK TKIs, and can be detected concomitantly. Functional assays confirmed that these alterations act as resistance mechanisms. These observations are of interest as PI3KCA/mTOR inhibitors may have a role in overcoming resistance. Citation Format: Giorgia Guaitoli, Francesco Facchinetti, Juan David Flórez-Arango, Floriane Braye, Hayato Mizuta, Santiago Ponce-Aix, Damien Vasseur, Ken André Olaussen, Stefan Michiels, Mihaela Aldea, Jordi Remon, Fabrice Barlesi, Benjamin Besse, David Planchard, Luc Friboulet. Alterations in PIK3CA/PTEN as resistance mechanisms in lung cancer patients progressing on first-line next generation EGFR/ALK tyrosine kinase inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3418.