To compare long-term survival after gastric cancer surgery between underweight (body mass index (BMI) <18.5), normal weight (BMI 18.5-24.9), overweight (BMI 25-29.9) and obese (BMI >30) patients.

Gastric cancer surgery is associated with significant morbidity. Obesity is a risk factor for short-term complications; however, previous studies on the role of body mass index (BMI) as a predictor of long-term survival are conflicting, and contemporary population-based data in the Western population are lacking.

This was a population-based, retrospective, nationwide cohort study in Finland using the Finnish National Esophago-Gastric Cancer Cohort (FINEGO). Gastrectomy patients with available height and weight data were included. A Cox regression model was used to calculate the 95% CI for 6 month to 5-year survival and 6 month survival adjusted for age, sex, year of surgery, Charlson comorbidity index, pathological p/yp stage, neoadjuvant therapy, type of resection and Lauren histological type.

In total, 1,647 patients undergoing gastrectomy for gastric cancer were identified. There were 64 (3.9%) underweight, 735 (44.6%) normal weight, 584 (35.5%) overweight, and 264 (16.0%) obese patients. In the first six months, mortality was higher in the overweight group (HR 1.663, 95% CI 1.158-2.389) compared to normal weight. However, 6 month to five-year mortality was highest in underweight patients (HR 1.426, 95% CI 1.019-1.994, compared to normal weight) and decreased with increasing BMI (HR.820, 95% CI.708-.949, overweight compared to normal weight). Obese patients had the best prognosis (HR.798 95% CI.655-.971).

In this population-based study, higher BMI was associated with better long-term survival after gastric cancer surgery, somewhat offset by higher mortality during first postoperative months, with obese patients having the best overall survival.