Assessment of methylated BCAT1 and IKZF1 circulating tumor DNA as a potential diagnostic and prognostic biomarker in esophagogastic cancers

348 Background: Esophagogastric cancers (EG cancers) are associated with high mortality and poor treatment outcomes due to advanced disease at diagnosis. Reliable non-invasive biomarkers are lacking for detection and prognostication. The aim of this study was to assess the clinical utility of methylated BCAT1 and IKZF1 circulating tumour DNA (ctDNA) for detection and prognosis of EG cancers. Methods: Blood samples were collected from patients diagnosed with either esophageal or gastric adenocarcinoma prior to commencing any treatment. DNA was extracted from plasma and analysed for methylation of BCAT1 and IKZF1, and ACTB as the reference gene, by multiplex qPCR. ctDNA positivity rates were assessed against cancer clinicopathological features using chi-squared tests and age-adjusted logistic regression with odds ratios (OR). Secondary outcome was overall survival after 12 months using cox-proportional hazard ratio (HR). Results: Ninety-seven patients (77/97 (79%) male; 70 (72%) with esophageal cancer and 27 (28%) with gastric cancer) were enrolled with median age 72 years (IQR = 61-79). Fifty-three (55%) were ctDNA positive. There was no difference between the ctDNA positivity rate of esophageal and gastric cancers (p > 0.05). Positivity was significantly associated with node positive tumours (N0 = 6/23 (20.7%), N1 = 5/10 (50%), N2 = 11/17 (64.7%), N3 = 3/4 (75%); p = 0.01) and depth of invasion (T1 = 0/9 (0%), T2 = 5/12 (41.7%), T3 = 17/36 (47.2%), T4 = 5/6 (83.3%), p = 0.049). ctDNA positivity was independent of history of GORD or Barrett’s disease (p > 0.05). There was a significant association between ctDNA and advanced stage disease (Stage I = 1/13 (7.7%), Stage II = 2/12 (16.7%), Stage III = 25/40 (62.5%), Stage IV = 25/32 (78.1%)), with stage IV cases having a 43-fold increased odds for a positive ctDNA result compared to stage I (OR = 43.1, 95%CI 4.7-392.0; p = 0.001). Patients testing positive for ctDNA had poorer overall survival outcomes compared to those testing negative (HR 4.23, 95% CI 1.84-9.68, p < 0.001). Conclusions: Our study demonstrates a potential role for methylated BCAT1 and IKZF1 ctDNA as a biomarker for the detection of EG cancers. The detection of ctDNA is significantly associated with poorer survival outcomes, with further studies warranted to determine whether ctDNA can be an independent predictor of survival. The integration of this ctDNA assay into clinical practice could further improve risk stratification, which may guide treatment strategies.