In this study, the multivariate Cox-hazard regression results supported our hypothesis that the one-year loss of skeletal muscle after gastrectomy (dSMI) is a significant predictor of overall survival along with preoperative muscle mass (SMA) and nutritional status (NRI) in stage 2 or 3 gastric cancer patients who survived longer than one year. Although several powerful prognostic factors for overall survival including recurrence, TNM stage, and comorbidity (HRs, 16.684, 1.298, and 1.262, respectively) were included in the multivariate analysis, the dSMI (HR 1.058), the preoperative SMA (HR 0.994) and preoperative NRI (HR 0.972) eventually remained as independent predictors. Kaplan-Meier curves also showed that less degree of postoperative muscle loss (small dSMI) and a better nutritional status before surgery (NRI) had a protective effect on the survival. The prognostic value of the two variables were maintained even in patients with relapsed tumor.
Nowadays, progressive loss of skeletal muscle mass has been highlighted as a prognostic factor in cancer patients, which is associated with cancer cachexia. Indeed, cachexia significantly contributes to mortality in patients with malignancy, accounting for more than 20% of cancer deaths 17. Especially, in patients with gastric cancer, sarcopenia is known to be highly prevalent 18,19, and a marked reduction in the initial body weight and muscle mass during the first postoperative year closely mimics the malnutrition and cancer cachexia cascade. Although several studies have reported preoperative sarcopenia as an indicator of poor prognosis, it may not reflect the steep deterioration after gastrectomy 16,20.
Our study, as a large-scale research, demonstrated that progressive muscle loss during the first year after gastrectomy is also a significant indicator of worse prognosis. Indeed, in a recent study based on a randomized multicenter trial, a marked loss in muscle or subcutaneous/visceral fat at 6 months after surgery could predict poor prognosis in patients with stage 2/3 gastric cancer 21. Although the study had a small number of population including patients not receiving adjuvant treatment, their results also demonstrated the prognostic importance of progressive muscle loss after gastric cancer surgery.
In terms of nutritional status, the preoperative NRI revealed its prognostic value in the recurrence group as well as whole patients. This result coincides with prior studies demonstrating that preoperative malnutrition could influence cancer-related or -unrelated death in malignancies 22,23. In contrast to our expectation, the change in NRI between before and one year after surgery (dNRI) did not influence the overall survival in gastric cancer patients. It might be attributed to the albumin homeostasis to balance albumin synthesis and catabolism or an active educational program instructing high-protein diet after surgery. However, our results should not hamper the importance of nutritional support for patients with gastric cancer.
Among several prognostic factors which were significant in this study, the dSMI and preoperative NRI could be valuable indicators because they have potentials to improve prognosis through efforts to enhance the nutritional status before surgery or maintain the muscle mass with intensive exercise and nutritional support after gastrectomy. Recently, exercise and physical activities during cancer treatment has been greatly emphasized in various malignancies, and the therapeutic benefit of exercise interventions on cancer patients have been investigated 24–27. In addition, in 2020, the American Cancer Society guidelines has been issued for diet and physical activity for cancer patients 28.
Only patients with stage 2 and 3 gastric cancer were included in the study because there is a discrepancy in treatment strategy and prognosis between stage 1 tumors and more advanced cancers. The vast majority of patients with stage 1 gastric cancers are treated with surgery alone and have an excellent prognosis of 5-year overall survival rate reaching to 95%. However, stage 2 and 3 cancers are indicated to surgery followed by chemotherapy, yielding the 3-year overall survival rate of 80.0%, and a significant number of patients experience relapse despite of adjuvant treatment 29,30. In this perspective, the prognostic implication of body composition and nutrition becomes higher in stage 2 and 3 gastric cancer.
We acknowledge that this study has some limitations. First, although data were collected prospectively in the registry, this is a retrospective study based on data from a single institution. Second, as we excluded patients who died within 1 year postoperatively, the prognostic effect of skeletal muscle loss was applicable to patients who survived longer than 1 year after surgery. Finally, despite prognostic relevance, the therapeutic benefit of efforts to support nutrition and preserve muscle mass was not proven. To overcome these limitations, a well-designed prospective multi-institutional study is required. Nevertheless, this study provides robust real-world evidence which is obtained from the large-scale study composed of 958 gastric cancer patients.