198P Use of chemotherapy and mismatch repair deficiency testing in resected stage II colon cancer

Abstract

Background Adjuvant chemotherapy for stage II colon cancer offers a small (2-3%) overall survival benefit and is not universally recommended. Currently, chemotherapy is often discussed with patients at increased recurrence risk based on histological criteria. Mismatch repair deficiency (dMMR) confers an improved prognosis and identifies patients who appear not to benefit from post-operative chemotherapy. Widespread immunohistochemistry testing in Australia began in 2013. Methods Prospective data were collected on all patients with resected stage II colon cancer between Feb-2010 to Feb-2015 across two large Australian hospitals. Rectal cancers were excluded. Data collected included patient demographics, tumour histology especially presence of high-risk features (<12 nodes, obstruction, perforation, poor differentiation, T4), dMMR testing frequency, chemotherapy use, and outcomes. Results 355 patients (56.1% female) were analysed. 25 (7.3%) received adjuvant chemotherapy (Cabrini 22/271 vs. Alfred 3/84,8% vs. 4%p = 0.22). Mean age was 77.9 years. No patient >80 years (52%) received chemotherapy. Presence of > 1 high-risk feature increased the likelihood of adjuvant chemotherapy. dMMR testing was performedon167patients(47%),mostoccurredpost-2013 (117/160vs. 50/195 patients).dMMRrateswere34.1%.2/57dMMRpatientsreceivedchemotherapy;both young(34and54years) withhigh-riskfeatures.28/355(7.8%) patientsrelapsed, including 3/25 (12%) who had received chemotherapy, and 25/330 (6.9%) who did not. 10/28(36%) ofrelapsesaredisease-freepost-resection,9(32%) alivewithmetastatic disease, and 9 deceased. An audit of familial cancer clinic referrals and BRAF mutation rate is underway. Conclusions >50%ofpatients were>80 years. Uptakeofchemotherapywaslow (7.3%).Despitethis,fewrelapseswereobserved(7.8%)and36%oftheseunderwent successful surgical salvage. dMMR testing should be performed in all stage II colon cancer patients being considered for adjuvant chemotherapy as it will identify a proportion(34.1%)ofpatientswhomaynotbenefitfromtreatment. Legal entity responsible for the study N/A Funding Alfred Hospital and Cabrini Health Disclosure All authors have declared no conflicts of interest.