Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

Incidence and clinicopathological characteristics of very young onset, young onset and late onset colorectal cancer in a culturally and linguistically diverse Sydney population (146472)

Alexandra Thoms 1 2 , Rebecca Nguyen 1 2 , Molly Nguyen 1 , Aimee Jansen 1 , Joseph Descellar 3 , Annette Tognela 1 , Weng Ng 1 3 4 , Aflah Roohullah 1 , Robert Yoon 1 , Wei Chua 1 3 4 , Stephanie H Lim 1 3 4
  1. Department of Medical Oncology, Liverpool and Campbelltown Hospitals, Sydney, NSW, Australia
  2. Sydney South West Clinical School, University of NSW, Sydney, NSW, Australia
  3. Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
  4. School of Medicine, University of Western Sydney, Sydney, NSW, Australia

Background

There is a rising incidence of sporadic young onset colorectal cancer (YOCRC), defined as those aged less than 50, with Australia having the highest rates globally. Current literature suggests YOCRC are more likely to present with advanced disease, left-sided tumours, and BRAF mutations. This retrospective analysis aimed to assess clinicopathological differences in very young (<35 years), young (36-49 years) and late onset (>50years) CRC.

Method

232 patients aged <50 years referred to Liverpool and Campbelltown Cancer Centres between 2013 to 2023 were included. Clinicopathological characteristics including demographics, histopathology, family history, genetics referral, treatment and outcomes were collected from electronic databases. This was compared to a historical database of 277 CRC patients aged >50. We also looked at incidence of YOCRC over 2 decades, in patients referred from 2005 to 2025.

Results

Of the 232 YOCRC patients, 56 patients (24%) were aged <35 and 176 patients (76%) aged between 36-49 years. 50% were culturally and linguistically diverse. At diagnosis, 5% were Stage I, 15% stage II, 50% stage III and 30% stage IV. 105 had BRAF testing with 8 (7%) positive for BRAFV600E mutation. 174 patients (75%) had left-sided tumours, with majority in sigmoid and rectum, 41 (17%) were mucinous or signet ring histology. 211 were tested for mismatch repair deficiency, with 21 (10%) mismatch-repair deficient. Consistent with available literature, our cohort showed a rising incidence of YOCRC over the last two decades, from 5% in 2005 to 20% in 2025.

Conclusion

Incidence of YOCRC is rising, with 1 in 4 patients of our contemporaneous cohort being very young. YOCRC appears to be predominantly left-sided, with a relatively high BRAF V600E mutation rate and mucinous/signet ring histology. Further analyses on treatment, germline testing and survival outcomes are ongoing, which will be correlated with the landscape in late onset CRC.