The patients in the current study with low HA-ESMs had significantly poorer OS rates and higher non-lung cancer-related mortality rates than those with high HA-ESMs in the lobectomy group, whereas no significant differences were found in the segmentectomy group. A low HA-ESM was an independent prognostic factor for OS in the lobectomy group but not in the segmentectomy group.

In the JCOG0802/WJOG4607L randomized trial, segmentectomy was superior to lobectomy in terms of OS for patients with small and peripheral NSCLC.5 It was hypothesized that segmentectomy, which preserves more lung parenchyma, may have allowed more extensive treatment of other diseases. Based on this concept, segmentectomy may be more beneficial for vulnerable patients with lower functional reserves than for healthy patients. In fact, several studies have indicated that patients with lower functional reserves benefit from sublobar resections. Mimae et al.18 demonstrated that older patients (age ≥80 years) had poorer prognoses than younger patients after wedge resections for early-stage NSCLC and that wedge resection could reduce mortality due to other causes. In the report, the author mentioned that segmentectomy for octogenarians did not reduce non-cancer-related mortality, and we performed the analysis of patients other than octogenarians. Isaka et al.19 reported that patients with high comorbidity indexes who underwent segmentectomies had better prognoses than those who underwent lobectomies because of reduced cumulative mortality due to respiratory diseases and other cancers. However, only one study has considered the clinical benefits of sublobar resections for patients with sarcopenia.20

To the best of our knowledge, the current study is the first to report that segmentectomy is superior to lobectomy for patients with low muscle mass, which includes many patients with sarcopenia. Because the poorer OS of patients with low HA-ESMs in the lobectomy group was caused by an increase in non-lung cancer-related mortality, the benefit of segmentectomy may be due to reduced non-lung cancer-related mortality.

In terms of lower functional reserves, there may be an overlap with old age, low respiratory function, high comorbidity rate, and low muscle mass. In the lobectomy group, the patients with low muscle mass had significantly worse %DLCO and tended to be older. However, after propensity-matching adjustments for age, respiratory function, and comorbidities, low muscle mass was a prognostic factor in the lobectomy group but not in the segmentectomy group. Although the lobectomy and segmentectomy groups comprised different cohorts, the patients with low muscle mass were more likely to benefit from segmentectomy than from lobectomy.

The reason for the aforementioned benefits of segmentectomy compared with lobectomy remains unclear. Previous studies have suggested that segmentectomy preserves respiratory function better than lobectomy.5,21 Theoretically, the load to the right heart is thought to be larger after lobectomy than after segmentectomy.22 In our study, preserving respiratory function and reducing the load on the right heart in the segmentectomy group may have contributed to an improved prognosis for the patients with low muscle mass. In fact, our results showed that cumulative mortality due to respiratory and cardiovascular diseases was significantly higher for the patients with low HA-ESMs than for those with high HA-ESMs in the lobectomy group.

Although current evidence supports resistance exercises for sarcopenia treatment, little evidence exists to show that treatment can improve postoperative prognoses.23 Nonetheless, a treatment with reduced invasion to the lung parenchyma might be a better option for patients with lung diseases and sarcopenia requiring lung resections.

Our study had several limitations. First, it was a retrospective single-center study. Therefore, selection bias likely existed due to the surgeons’ patient selection process. Additionally, the cutoff value was calculated at our institution, and its appropriateness could not be confirmed. Future multicenter studies are warranted to reduce selection bias and set an appropriate cutoff value.

Second, in this study, we did not adopt the sarcopenia definition per the European Working Group on Sarcopenia in Older People (EWGSOP2). The guidelines demonstrate that probable sarcopenia is first identified by low muscle strength and next confirmed by low muscle quantity.6 Instead, we used HA-ESM as an indicator of muscle loss because we could not obtain data on muscle strength. Although using CT imaging is thought to be acceptable in cancer research, muscle strength is necessary for formal diagnosis of sarcopenia. A prospective observational study including muscle strength evaluation is needed for further understanding.

Third, due to the small number of patients and differences in patient backgrounds, we could not perform a direct comparison between lobectomy and segmentectomy.

In conclusion, patients with low muscle mass deemed to be at risk are more likely to benefit from segmentectomies than from lobectomies in terms of mortality due to other causes. When feasible, surgical procedures should be selected considering not only the patient’s age, respiratory function, and morbidities, but also the patient’s muscle mass.