Esophageal squamous cell carcinoma (ESCC) is one of the most prevalent and aggressive cancers in the elderly population, significantly affecting both survival rates and quality of life (1–3). As the global population ages, there is an increasing trend of older patients being diagnosed with esophageal cancer, which makes the management of these patients an area of growing concern (4–6). Surgical resection, particularly esophagectomy, remains a cornerstone in the treatment of localized ESCC, with the potential for curative outcomes. However, this complex surgical procedure is associated with high perioperative risks and can have a considerable impact on postoperative recovery, particularly in elderly patients (7–9). The treatment approach for ESCC typically combines surgery with neoadjuvant therapy, such as chemotherapy or chemoradiotherapy, followed by adjuvant treatments based on pathological results and the individual patient’s condition (10–12). This multimodal approach is consistent with the recommendations in current clinical guidelines, including those from the National Comprehensive Cancer Network (NCCN) and the Chinese Anti-Cancer Association (CACA) (13–15).

Body Mass Index (BMI), a widely recognized indicator of nutritional status and general health, has been studied in the context of various cancers, due to its potential influence on surgical outcomes, complications, and long-term survival (16–18). Nutritional status plays a crucial role in both survival and prognosis, with adequate nutrition being necessary for recovery and the management of cancer. BMI is one of the objective indicators that reflects the nutritional status of patients. While obesity is generally considered a risk factor for multiple comorbidities, including cardiovascular and metabolic diseases, low BMI and malnutrition are also associated with poor prognosis in cancer patients. Given the heterogeneity within the elderly population, it is essential to determine whether BMI serves as an independent prognostic factor, or if other factors such as frailty, comorbid conditions, and treatment strategies play a more substantial role in influencing outcomes.

This study seeks to address the knowledge gap regarding the impact of BMI on the postoperative outcomes of elderly patients with ESCC following esophagectomy. Through this analysis, we hope to provide critical insights that can guide clinical decision-making for elderly ESCC patients undergoing esophagectomy.

This study aimed to evaluate the impact of BMI on the postoperative outcomes of elderly patients with ESCC following esophagectomy. Outcomes showed no significant differences in OS and DFS among the BMI groups (normal, low, and high BMI). These findings suggest that while BMI is a recognized indicator of nutritional status and health, it may not independently predict long-term survival outcomes in elderly ESCC patients who undergo esophagectomy (Figure 5).

There were no significant differences in preoperative characteristics between patients with normal and low BMI, while patients with high and low BMI showed no significant differences in various indicators except for the administration of neoadjuvant therapy. Neoadjuvant therapy, as supported by findings from NEOCRTEC5010, has demonstrated significant advantages in extending survival time and reducing postoperative tumor recurrence without increasing postoperative complication rates or perioperative mortality (25). This advantage explains why our study did not perform further propensity score matching (PSM) to adjust for these differences in neoadjuvant treatment across BMI groups.

Interestingly, however, patients with a low BMI experienced significantly higher incidences of several specific postoperative complications, including pulmonary infections, hydrothorax, respiratory failure, heart failure, and chylous fistula compared to those with normal or high BMI. These findings highlight the heightened vulnerability of underweight patients to certain adverse events, possibly due to diminished physiological reserves and poorer nutritional status, which can impair recovery and increase susceptibility to complications (16–18).

In line with these findings, a study from Japan reveals a nuanced U-shaped association between BMI and outcomes such as mortality and major complications, highlighting that patients with both low and high BMI are at increased risk. Importantly, severely underweight individuals (BMI <16.0 kg/m²) exhibited a more than twofold increase in mortality risk, underscoring the vulnerability linked to low BMI. Conversely, obesity (BMI ≥27.5 kg/m²) also elevated mortality risk, though to a lesser extent. This indicates that extremes in BMI can contribute to poorer outcomes following esophagectomy in ESCC patients. Moreover, the study identified a reverse J-shaped relationship between BMI and failure to rescue, suggesting that lower BMI patients face greater challenges in recovery after major complications arise. This emphasizes the need for meticulous nutritional and postoperative care, especially for underweight patients, to improve resilience to postoperative complications. Ensuring adequate nutritional support and monitoring in the perioperative period could potentially mitigate the elevated risks associated with low BMI. For patients with high BMI, weight management strategies and careful monitoring for obesity-related complications could be beneficial (26).

In Mitzman et al.'s study, significant differences were observed across BMI categories for seven out of nine types of complications. Specifically, underweight and obesity class III patients were associated with an increased rate of complications. Conversely, individuals in the overweight and obesity class I categories tended to have a reduced risk for most types of complications. These insights align with our study’s results, reinforcing the notion that while BMI does not independently predict long-term survival outcomes in elderly ESCC patients undergoing esophagectomy, it does have a notable impact on the risk of postoperative complications. This highlights the complexity of BMI’s role, underscoring the importance of a comprehensive preoperative assessment that considers BMI as one of several factors influencing patient outcomes (27).

The prognostic significance of BMI in esophageal cancer remains controversial. Several previous reports have described an “obesity paradox,” in which overweight or mildly obese patients show improved survival compared to those with normal or low BMI, potentially due to greater nutritional reserves and better tolerance of surgical and adjuvant treatments. In contrast, other studies have reported that both low and high BMI are associated with worse survival, showing a U-shaped or reverse J-shaped relationship between BMI and mortality. Still, a number of studies—like ours—have found no clear survival differences between BMI categories. This variability across studies underscores the complexity of BMI as a prognostic factor in esophageal cancer. The relationship between BMI and prognosis in esophageal cancer should be interpreted in light of body composition rather than BMI alone. BMI does not distinguish between lean mass and fat mass, and low muscle mass (sarcopenia) has been independently linked to worse cancer outcomes. Future studies incorporating skeletal muscle measurements from CT imaging or bioelectrical impedance could help clarify whether muscle depletion, rather than low BMI per se, drives poor outcomes. Moreover, standardizing BMI cutoff values based on regional population characteristics may improve comparability across studies. Multicenter prospective research is warranted to disentangle the interplay of nutritional status, physiological reserve, and metabolic health in determining both perioperative safety and long-term prognosis.

The comparable distribution of stage III-IV disease—and the lack of a significantly higher proportion of stage IV cancer in the low-BMI group—strongly suggests that pretreatment low BMI in our elderly ESCC cohort did not predominantly stem from significantly more advanced tumor burden. This is noteworthy given our routine practice of preoperative nutritional optimization for patients with low BMI or poor nutritional status, which likely mitigated the impact of any existing tumor-related obstruction on nutritional parameters at the time of surgery. Therefore, the observed significantly higher rates of specific postoperative complications (pulmonary infections, hydrothorax, respiratory failure, heart failure, chylous fistula) in the low-BMI group appear less likely to be primarily driven by differences in tumor stage at the time of surgery. Instead, these complications seem more directly attributable to the physiological vulnerability associated with a low BMI itself, such as diminished physiological reserves and poorer baseline nutritional status, as previously hypothesized [16-18]. This aligns with the concept highlighted in the Japanese study [26] regarding the heightened challenges in recovery (failure to rescue) faced by underweight patients. While our nutritional interventions prior to surgery were essential, they may not have fully reversed the underlying frailty associated with chronic low BMI in the short preoperative window. In our cohort, we observed a notable imbalance in BMI distribution, with the majority of patients (approximately 75%) classified as having a normal BMI. This raises the question: Is it appropriate to directly apply the WHO BMI classification—developed primarily for Western populations—to East Asian populations without modification? While the suitability of WHO criteria for Asian populations, particularly Chinese individuals, remains debated, no universally accepted, unified BMI classification standard specific to Asian/Chinese populations currently exists. Importantly, Chinese clinical and nutritional guidelines, such as those issued by the Chinese Nutrition Society, continue to adopt the WHO BMI criteria [28]. To maintain consistency with domestic guideline-based practice and facilitate comparability with existing literature, we adhered to the WHO classification in this study. However, we acknowledge the objective limitations of applying categorical cutoffs that may not fully capture the nuances of BMI-outcome relationships in East Asian populations. To address this concern and reduce potential misclassification bias, we supplemented our categorical analysis with restricted cubic spline (RCS) analyses. These analyses allowed us to model BMI as a continuous variable, providing a more detailed characterization of its association with OS, DFS, and postoperative complications across its entire range (Figures 2C, 2D, and 3D). The RCS curves offer a visual and statistical interpretation beyond predefined categories, helping to elucidate potential non-linear relationships and mitigate concerns about the applicability of WHO cutoffs.

This study have several limitations. Firstly, as a retrospective cohort study, it is subject to inherent biases related to data collection and patient selection, which may affect the generalizability of the findings. Additionally, the study relies on data from a single institution, which may not be representative of wider populations or different healthcare settings. Another limitation is the reliance on BMI as the sole indicator of nutritional status, which does not account for other factors such as muscle mass or distribution of body fat, potentially limiting the comprehensiveness of assessing patients’ nutritional and health status. Furthermore, the study does not account for potential confounding factors such as socioeconomic status or lifestyle factors that could influence both BMI and cancer outcomes. Further research is warranted to explore these complex interactions and inform more personalized treatment approaches.

In conclusion, outcomes suggested that BMI, despite being a key indicator of nutritional status, does not significantly influence OS or DFS in this patient population. Although there were no substantial differences in survival outcomes across BMI categories, patients with low BMI exhibited higher incidences of certain postoperative complications, such as pulmonary infections and chylous fistula.