Abstract 4898: Clinical application of quantitative multiplex mass spectrometry-based proteomics in predicting clinical outcomes in locally advanced rectal cancer

Background: Neoadjuvant chemoradiotherapy (CRT) using 5-fluorouracil (5-FU) is a standard treatment for locally advanced rectal cancer (LARC) to improve clinical outcomes. The pathologic responses after neoadjuvant CRT is a major prognostic factor, thus identification of good or poor responder in advance is important. This study is to find candidate predictive biomarkers for CRT and prognosis in LARC patients using quantitative mass spectrometry (MS). Materials and methods: 86 patients with stage II/III LARC, received neoadjuvant CRT consisting of 5-FU/leucovorin followed by surgery were included. 14 proteins potentially associated with 5-FU activity or prognosis were evaluated in archived formalin-fixed, paraffin-embedded pre- and post-CRT tumor tissues using MS: DHFR, DPYD, EGFR, hENT1, Her2, MET, OPRT, p16, TK1, TYMP, TYMS, UCK1, UCK2, UPP1. Tumor regression grade (TRG) after CRT was assessed by Dworak criteria: 0, no regression; 1, dominant tumor mass with obvious fibrosis; 2, dominant fibrotic changes with few tumor cells; 3, very few tumor cells; 4, no tumor cells. Results: TGR was 0 in 2 (2.3%), 1 in 30 (34.9%), 2 in 23 (26.7%), 3 in 20 (23.3%), and 4 in 11(12.8%) patients. Major regression (TRG 2/3/4) was associated with high TK1 ( P = 0.040), low TYMS ( P = 0.037), p16 ( P = 0.055), and UPP1 ( P = 0.028) levels. Among the pre-CRT parameters, low CEA level ( P = 0.013), clinical stage II ( P P = 0.052), low EGFR level ( P =0.006), undetectable TYMS level ( P = 0.070) were associated with longer recurrence-free survival (RFS). Among the post-CRT parameters, major pathologic response ( P = 0.001), and the absence of lymphatic ( P P = 0.025)/ perineural invasion ( P = 0.001) was associated with longer RFS. For 71 patients with available paired pre- and post-CRT tissues, the changes of protein expression were calculated. The pre-CRT/post-CRT ratio of DHFR (>1.1), Her2 ( P = 0.008) and pre-CRT high EGFR level (≥200amol/ug; HR=2.23; 95% CI, 1.03-4.83; P = 0.042) were significantly associated with shorter RFS. The presence of lymphatic invasion ( P =0.005), positive pre-CRT TYMS level ( P = 0.008), and high CEA level ( P = 0.015) were significantly related to short survival. Conclusions: Quantitative MS-based proteomics can facilitate the identification of predictive biomarkers of CRT responses and prognosis in LARC patients. Citation Format: Ho Jung An, Ji-Han Jung, Byoung Yong Shim, Hyung Soon Park, Hyeon-Min Cho, Hyung-Jin Kim, Ri Na Yoo, Sung Hwan Kim, Jonghoon Lee, Kang-Moon Lee, Dae Bum Kim, Ji Min Lee. Clinical application of quantitative multiplex mass spectrometry-based proteomics in predicting clinical outcomes in locally advanced rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4898.