Clinical utility of targeted next generation sequencing (NGS) to predict response to neoadjuvant therapy (NT) in rectal cancer (RC).

Abstract

237 Background: NGS analysis has identified molecular alterations that have predictive and prognostic implications in advanced RC. However, its role in identifying predictive signatures of chemoradiotherapy response in RC remains largely unexplored. Neoadjuvant rectal cancer (NAR) score, a composite score available after resection, is a validated short-term surrogate endpoint for long-term outcomes. Herein, we identified gene alterations in early stage RC with NGS analysis and correlated mutations with tumor response using the NAR scoring system. Methods: Patients (pts) with stage I-III RC completing NT followed by resection (2011-2018) had their tumor prospectively sequenced by an ion torrent targeted 22 gene NGS panel ( AKT1, ALK, BRAF, CTNNB1, DDR2, EGFR, ERBB2/4, FBXW7, FGFR1/2/3, KRAS, MAP2K1, MET, NOTCH1, NRAS, PIK3CA, PTEN, SMAD4, STK11, TP53). NAR scores were calculated based on clinical and pathologic staging data input, yielding 3 cohorts: low (score < 8, pCR or near CR), intermediate (8-16), or high ( > 16, poor or no response) NAR scores. Associations were drawn using Two-sided Fisher’s exact. Both unadjusted (p) and Benjamini & Hochberg adjusted (BHp) p-values are shown. Results: 51 pts with RC were analyzed: median age 59 (24-81), male (59%), clinical stage I (6%), II (25%) and III (69%). Pathological mutations were found in 94% of pts, including TP53 (76%), KRAS (49%), PIK3CA (10%), NRAS (6%), FGFR3 (4%), MET (4%). Post NT 8 (16%) pts had low NAR scores, including 6 (12%) cases with pCR, 26 (51%) intermediate, and 17 (33%) high NAR scores. Gene alterations in FGFR3 (p =0.022, BHp = 0.15) and NRAS (p =0.026, BHp = 0.15) were associated with NAR score, while no differences were observed with mutations in TP53 or KRAS. Additionally, 17 (33%) pts had recurrences [13% of pts with low NAR scores, 31% intermediate, 47% high], with metastases primarily to lung (53%) and/or liver (35%). Conclusions: This study suggests that pts with RC who derived favorable responses to standard NT could have a targeted molecular profile, namely alterations in FGFR3 and NRAS. Conversely, pts that lack this profile may benefit from novel therapeutic approaches to improve NAR scores and long-term outcomes.