Background and Aims: A concerning rise in incidence of young-onset cancers globally led to the examination of trends in incidence and survival of gastrointestinal (GI) adenocarcinomas in the Northern Territory (NT), Australia, over a 28-year period, with a special emphasis on Indigenous peoples. Methods: This cross-sectional analysis of a prospective longitudinal database, NT Cancer Registry (1990–2017), includes all reported cases of GI (oesophagus, gastric, small intestinal, pancreas, colon, and rectum) adenocarcinomas. Poisson regression was used to estimate incidence ratio ratios, and survival was modelled using Cox proportional hazard models separately for people aged 18–50 years and >50 years. Results: A total of 1608 cases of GI adenocarcinoma were recorded during the time of the study. While the overall incidence in people 18–50 years remained unchanged over this time (p = 0.51), the rate in individuals aged >50 years decreased (IRR = 0.65 (95% CI 0.56–0.75; p < 0.0001)). Incidence rates were significantly less in females >50 years (IRR = 0.67 95% CI 0.59–0.75; p < 0.0001), and their survival was significantly better (HR = 0.84 (95%CI 0.72–0.98; p < 0.03)) compared to males. Overall survival across all GI subsites improved in both age cohorts, especially between 2010 and 2017 (HR = 0.45 (95%CI 0.29–0.72; p < 0.0007) and HR = 0.64 (95%CI 0.52–0.78; p < 0.0001), respectively) compared to 1990–1999, driven by an improvement in survival in colonic adenocarcinoma alone, as the survival remained unchanged in other GI subsites. The incidence was significantly lower in Indigenous patients compared to non-Indigenous patients, in both age cohorts (18–50 years IRR = 0.68 95% CI 0.51–0.91; p < 0.009 and >50 years IRR = 0.48 95% CI 0.40–0.57; p < 0.0001). However, Indigenous patients had worse survival rates (18–50 years HR = 2.06 95% CI 1.36–3.11; p < 0.0007 and >50 years HR = 1.66 95% CI 1.32–2.08; p < 0.0001). Conclusions: There is a trend towards an increased incidence of young-onset GI adenocarcinomas in the NT. Young Indigenous patients have lower incidence but worse survival across all GI subsites, highlighting significant health inequities in life expectancy. Targeted, culturally safe Indigenous community-focussed programs are needed for early detection and patient-centred management of GI adenocarcinomas.

3579 Background: Recurrence of colorectal cancer has been linked to the presence of epigenetic circulating tumour DNA (ctDNA) in patient plasma after surgery. The prognostic significance of ctDNA prior to treatment remains unknown. This study investigated the correlation between pre-treatment ctDNA and current radiological (MRI) prognostic markers in patients with rectal cancer. Methods: Forty-two patients with rectal cancer were enrolled, with all having staging MRI prior to treatment. Plasma was taken for ctDNA at diagnosis. The presence of either methylated branched-chain amino acid transaminase 1 (BCAT1) or Ikaros family zinc finger (IKZF1) in cell-free DNA from plasma was deemed a positive ctDNA result. Correlation of MRI prognostic indicators and ctDNA results was assessed with chi-square tests. Univariable and multivariable cox regression analyses were performed to determine variables associated with overall survival (OS). Results: Mean age was 64.4 years (SD 12.5) and majority were male (30/42, 71.4%). 11, 13, 9 & 9 patients had stages I, II, III, IV respectively. Patients had a minimum follow-up of 36 months. Thirty-three (78.6%) patients received neoadjuvant chemoradiotherapy. 29 (69.0%) patients underwent surgical resection. 3-year survival rate was 64% in the overall group. 67% (n=28/42) of patients were positive for the methylated ctDNA at diagnosis. 11 out of 12 patients with a positive circumferential resection margin (CRM +) were ctDNA positive (p=0.03). Univariable analysis showed that prognostic indicators for OS were presence of extramural venous invasion (EMVI) (HR 3.0, 95% CI 1.1-8.4), CRM+ (HR 12.2, 95%CI 3.9-37.6), metastatic disease (HR 7.32, 95% CI 2.63-20.37) and ctDNA% methylation (HR 1.1, 95% CI 1.04-1.13) (Table 1). The presence of CRM+ and a positive ctDNA had a HR of 20.5 (95% CI 5.1-82.3). With multivariable analysis, including adjustment for age and EMVI, only CRM+/ctDNA+ variable was an independent predictor for poor survival (HR 20.2, 95% CI 4.5-90.9). Conclusions: In rectal cancer, almost all patients with CRM involvement have ctDNA, and these patients had the worst prognosis. Future studies with longitudinal ctDNA assessment pre and post treatment could potentially inform prognosis and help tailor patients’ treatment.[Table: see text]

An overabundance of desmoplasia in the tumour microenvironment (TME) is one of the defining features that influences pancreatic ductal adenocarcinoma (PDAC) development, progression, metastasis, and treatment resistance. Desmoplasia is characterised by the recruitment and activation of fibroblasts, heightened extracellular matrix deposition (ECM) and reduced blood supply, as well as increased inflammation through an influx of inflammatory cells and cytokines, creating an intrinsically immunosuppressive TME with low immunogenic potential. Herein, we review the development of PDAC, the drivers that initiate and/or sustain the progression of the disease and the complex and interwoven nature of the cellular and acellular components that come together to make PDAC one of the most aggressive and difficult to treat cancers. We review the challenges in delivering drugs into the fortress of PDAC tumours in concentrations that are therapeutic due to the presence of a highly fibrotic and immunosuppressive TME. Taken together, we present further support for continued/renewed efforts focusing on aspects of the extremely dense and complex TME of PDAC to improve the efficacy of therapy for better patient outcomes.

BackgroundColorectal cancer with synchronous liver‐only metastasis is managed with a multimodal approach, however, optimal sequencing of modalities remains unclear.MethodsA retrospective review of all consecutive rectal or colon cancer cases with synchronous liver‐only metastasis was conducted from the South Australian Colorectal Cancer Registry from 2006 to 2021. This study aimed to investigate how order and type of treatment modality affects overall survival.ResultsData of over 5000 cases were analysed (n = 5244), 1420 cases had liver‐only metastasis. There were a greater number of colon than rectal primaries (N = 1056 versus 364). Colonic resection was the preferred initial treatment for the colon cohort (60%). In the rectal cohort, 30% had upfront resection followed by 27% that had chemo‐radiotherapy as 1st line therapy. For the colon cohort, there was an improved 5‐year survival with surgical resection as initial treatment compared to chemotherapy (25% versus 9%, P < 0.001). In the rectal cohort, chemo‐radiotherapy as the initial treatment was associated with an improved 5‐year survival compared to surgery or chemotherapy (40% versus 26% versus 19%, P = 0.0015). Patients who were able to have liver resection had improved survival, with 50% surviving over 5 years compared to 12 months in the non‐resected group (P < 0.001). Primary rectal KRAS wildtype patients who underwent liver resection and received Cetuximab had significantly worse outcomes compared to KRAS wildtype patients who did not (P = 0.0007).ConclusionsWhere surgery is possible, resection of liver metastasis and primary tumour improved overall survival. Further research is required on the use of targeted treatments in patients undergoing liver resection.