Immunohistochemistry testing for mismatch repair deficiency in Stage 2 colon cancer: A cohort study of two cancer centres.
BACKGROUND/OBJECTIVES
Adjuvant chemotherapy for Stage II colon cancer offers a small (2-3%) overall survival benefit and is not universally recommended. Mismatch repair deficiency (dMMR) confers an improved prognosis identifying patients unlikely to benefit from adjuvant chemotherapy. The aim of this study was to investigate the use of dMMR immunohistochemistry in two major cancer treatment centres.


METHODS
Prospective data were collected on all patients with resected Stage II colon cancer between 2010 and 2015 across two large Australian hospitals. Data collected included patient demographics, tumour histology, dMMR immunohistochemistry, chemotherapy use, and outcomes.


RESULTS
All 355 patients (56.1% female, median age 81) with resected Stage 2 Colon cancer entered on to the surgical database were included in this analysis. MMR testing was performed on 167 patient samples (47%), most occurred post-2013 (73.1% vs. 26.9% patients). dMMR rates were 34.1%. 25 (7.3%) received adjuvant chemotherapy, with no patient >80 years receiving treatment. Presence of ≥2 high-risk feature increased the likelihood of adjuvant chemotherapy. Only 3.6% dMMR patients received chemotherapy; both were young with high-risk features. 27/288 (7.6%) patients (with follow up) relapsed, with 7 disease-free post-resection of metastatic disease, 9 are alive with metastatic disease, and 11 deceased.


CONCLUSIONS
Unlike clinical trial populations, Stage 2 colon cancer patients are often elderly, have high rates of dMMR tumours, are rarely offered chemotherapy, yet still have excellent outcomes. dMMR immunohistochemistry is being increasingly used to identify Stage 2 patients who do not require chemotherapy.
['Grant|Matthew|M|', 'Haydon|Andrew|A|', 'Au|Lewis|L|', 'Wilkins|Simon|S|', 'Oliva|Karen|K|', 'Segelov|Eva|E|', 'Antill|Yoland|Y|', 'Carne|Peter|P|', 'Ranchod|Pravin|P|', 'Polglase|Adrian|A|', 'Farmer|Chip|C|', 'Chin|Martin|M|', 'Wale|Roger|R|', 'Simpson|Paul|P|', 'Bell|Stephen|S|', 'Skinner|Stewart|S|', 'McMurrick|Paul|P|', 'Shapiro|Jeremy|J|']
D000368:Aged D000369:Aged, 80 and over D001315:Australia D001932:Brain Neoplasms D017024:Chemotherapy, Adjuvant D003110:Colonic Neoplasms D015179:Colorectal Neoplasms D053843:DNA Mismatch Repair D005260:Female D006801:Humans D007150:Immunohistochemistry D008297:Male D008875:Middle Aged D009367:Neoplasm Staging D009386:Neoplastic Syndromes, Hereditary D018579:Patient Selection D011379:Prognosis D011446:Prospective Studies D016896:Treatment Outcome
Immunohistochemistry Mismatch repair deficiency Chemotherapy Colorectal cancer