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Mismatch Repair Deficiency, Microsatellite Instability, and Survival: An Exploratory Analysis of the Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) Trial
Smyth EC, Wotherspoon A, Peckitt C, Gonzalez D, Hulkki-Wilson S Eltahir Z, et al.
Importance: Mismatch repair (MMR) deficiency (MMRD) and microsatellite instability (MSI) are prognostic for survival in many cancers and for resistance to fluoropyrimidines in early colon cancer. However, the effect of MMRD and MSI in curatively resected gastric cancer treated with perioperative chemotherapy is unknown.
Objective: To examine the association among MMRD, MSI, and survival in patients with resectable gastroesophageal cancer randomized to surgery alone or perioperative epirubicin, cisplatin, and fluorouracil chemotherapy in the Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) trial.
Design, Setting, and Participants: This secondary post hoc analysis of the MAGIC trial included participants who were treated with surgery alone or perioperative chemotherapy plus surgery for operable gastroesophageal cancer from July 1, 1994, through April 30, 2002. Tumor sections were assessed for expression of the MMR proteins mutL homologue 1, mutS homologue 2, mutS homologue 6, and PMS1 homologue 2. The association among MSI, MMRD, and survival was assessed.
Main Outcomes and Measures: Interaction between MMRD and MSI status and overall survival (OS).
Results: Of the 503 study participants, MSI results were available for 303 patients (283 with microsatellite stability or low MSI [median age, 62 years; 219 males (77.4%)] and 20 with high MSI [median age, 66 years; 14 males (70.0%)]). A total of 254 patients had MSI and MMR results available. Patients treated with surgery alone who had high MSI or MMRD had a median OS that was not reached (95% CI, 11.5 months to not reached) compared with a median OS among those who had neither high MSI nor MMRD of 20.5 months (95% CI, 16.7-27.8 months; hazard ratio, 0.42; 95% CI, 0.15-1.15; P = .09). In contrast, patients treated with chemotherapy plus surgery who had either high MSI or MMRD had a median OS of 9.6 months (95% CI, 0.1-22.5 months) compared with a median OS among those who were neither high MSI nor MMRD of 19.5 months (95% CI, 15.4-35.2 months; hazard ratio, 2.18; 95% CI, 1.08-4.42; P = .03).
Conclusions and Relevance: In the MAGIC trial, MMRD and high MSI were associated with a positive prognostic effect in patients treated with surgery alone and a differentially negative prognostic effect in patients treated with chemotherapy. If independently validated, MSI or MMRD determined by preoperative biopsies could be used to select patients for perioperative chemotherapy.
Commentary by Prof Lordick and Dr Elizabeth Smyth
How understanding the interaction between specific molecular subgroups and current treatment standards can help to select gastric cancer patients for perioperative chemotherapy is provided in a manuscript describing the relationship between mismatch repair status, perioperative chemotherapy and survival in the MAGIC trial (Smyth et al.). Patients who had operable mismatch repair deficient tumours (8% of gastric cancers), had excellent survival when treated with surgery alone, but did not appear to benefit from perioperative chemotherapy, unlike patients with mismatch repair proficient tumours. This was a retrospective analysis of a prospective clinical trial, and although not practice changing, is thought provoking. More research is required to determine what the best treatment for patients with operable mismatch repair deficient gastric cancer; as immuno-oncology treatments have demonstrated excellent response rates in other mismatch repair deficient tumours, this could be an interesting option to explore.