Carcinoma Microsatellite Instability Status as a Predictor of Benefit from Fluorouracil-Based Adjuvant Chemotherapy for Stage II Rectal Cancer

Purpose: Rectal cancers with high microsatellite-instable have clinical and pathological features thatdifferentiate them from microsatellite-stable or low- frequency carcinomas, which was studied rarely in stageII rectal cancer, promoting the present investigation of the usefulness of microsatellite-instability status asa predictor of the benefit of adjuvant chemotherapy with fluorouracil in stage II rectal cancer. Patients and
Methods: Data of 460 patients who underwent primary anterior resection with a double stapling technique forrectal carcinoma at a single institution from 2008 to 2012 were retrospectively collected. All patients experienceda total mesorectal excision (TME) operation. Survival analysis were analyzed using the Cox regression method.
Results: Five-year rate of disease-free survival (DFS) was noted in 390 (84.8%) of 460 patients with stage II rectalcancer. Of 460 tissue specimens, 97 (21.1%) exhibited high-frequency microsatellite instability. Median age ofthe patients was 65 (50-71) and 185 (40.2%) were male. After univariate and multivariate analysis, microsatelliteinstability (p= 0.001), female sex (p< 0.05) and fluorouracil-based adjuvant chemotherapy (p< 0.001), the 3 factorswere attributed to a favorable survival status independently. Among 201 patients who did not receive adjuvantchemotherapy, those cancers displaying high-frequency microsatellite instability had a better 5-year rate of DFSthan tumors exhibiting microsatellite stability or low-frequency instability (HR, 13.61 [95% CI, 1.88 to 99.28];p= 0.010), while in 259 patients who received adjuvant chemotherapy, there was no DFS difference betweenthe two groups (p= 0.145). Furthermore, patients exhibiting microsatellite stability or low-frequency instabilitywho received adjuvant chemotherapy had a better 5-year rate of DFS than patients did not (HR, 5.16 [95% CI,2.90 to 9.18]; p< 0.001), while patients exhibiting high-frequency microsatellite instability were not connectedwith increased DFS (p= 0.696). It was implied that female patients had better survival than male.
Conclusion:Survival status after anterior resection of rectal carcinoma is related to the microsatellite instability status,adjuvant chemotherapy and gender. Fluorouracil-based adjuvant chemotherapy benefits patients of stage IIrectal cancer with microsatellite-stable or low microsatellite-instable, but not those with high microsatelliteinstable.Additionally, free of adjuvant chemotherapy, carcinomas with high microsatellite-instable have a better5-year rate of DFS than those with microsatellite-stable or low microsatellite-instable, and female patients havea better survival as well.