Esophageal cancer is the eighth most common cancer worldwide and is associated with poor outcomes (1). Neoadjuvant treatment, such as neoadjuvant chemotherapy (NAC) and neoadjuvant chemoradiotherapy (CRT), has been widely adopted as a standard treatment for esophageal cancer (2,3). However, neoadjuvant treatment can cause malnutrition, immunodeficiency, and sarcopenia, which increase the risk of severe postoperative complications (4-6). In particular, it is well known that postoperative infectious complications, such as anastomosis leakage, pneumonia, etc., have a negative impact on the overall postoperative survival of esophageal cancer patients. Booka et al. reported in a meta-analysis study that postoperative complications after esophagectomy, include pulmonary complications, anastomotic leakage, and decreased long-term survival (7). In addition, poor nutritional status, depression of the immune system, and severe muscle depletion induced by surgical stress cause infection and delayed wound healing, often resulting in longer hospital stays and higher readmission and mortality rates (8). Although increasing efforts have been made to elucidate the predictors of postoperative infection-associated morbidities and to improve the outcomes of patients with esophageal cancer, to our knowledge no studies of patients with esophageal cancer undergoing neoadjuvant treatment have focused on the association between postoperative infectious complications, changes in nutritional and immunological status, and sarcopenia. In this study, we evaluated changes in nutritional status, immune-inflammatory status, and skeletal muscle mass during neoadjuvant chemotherapy in patients with esophageal cancer and examined the association between these factors and postoperative infectious complications.

Study population and ethical considerations. Between January 2014 and November 2019, 280 consecutive patients with esophageal cancer underwent esophagectomy with curative intent by right thoracotomy or thoracoscopy with 2- or 3-field lymph node dissection at Shizuoka General Hospital. Among them, the following patients were excluded: those who underwent esophagectomy and laryngopharyngectomy (n=8), those who underwent esophagectomy without reconstruction (n=2), those who underwent salvage esophagectomy (n=5), those who died within 5 days postoperatively attributable to cardiovascular events, bleeding, or unknown causes (n=4), those who underwent synchronous liver or colon cancer surgery (n=3), and those who underwent reconstruction using the jejunum or colon as a conduit (n=4). After excluding these 26 patients, 254 patients were diagnosed with the following conditions based on pathological analysis: squamous cell carcinoma (SCC), 212 patients; adenocarcinoma, 38; malignant melanoma, one; mucoepidermoid carcinoma, one; neuroendocrine carcinoma, one; and carcinosarcoma, one. During the study period, in Japan, preoperative combination chemotherapy with cisplatin and 5-fluorouracil (CF) followed by curative surgery was the standard therapy for clinical stage II or III advanced esophageal SCC (9). Among the 212 patients with esophageal SCC, 138 were diagnosed as clinical stage II or III. After 15 patients who had received chemotherapy other than CF were excluded, 123 patients who had undergone esophagectomy after combination chemotherapy with CF were eligible for this study. The study followed the ethical guidelines for human subjects of the Institutional Review Board of Shizuoka General Hospital and was approved by the Board (SGHIRB#2019069). The need to obtain informed consent was waived owing to the retrospective nature of this study.

Neoadjuvant treatment protocols. Patients received two courses of NAC with CF, with an inter-treatment interval of 3-4 weeks. Intravenous cisplatin was administered at a dose of 80 mg/m² on day 1, and 5-fluorouracil was administered at a dose of 800 mg/m²/day by continuous infusion for 24 h on days 1-5 unless contraindicated. When adverse events, such as significant myelosuppression or renal dysfunction were observed, the doses of the chemotherapy agents were reduced or stopped, and surgery was performed without a second course. In this study, patients who failed to complete two courses of NAC and required a dose reduction of CF were also included. All patients underwent surgery at least 3-4 weeks after the completion of NAC.

Surgical procedures. Open thoracic, thoracoscopic, or robotic esophagectomy were performed in all cases. Thoracoscopic and robotic esophagectomies were introduced in our hospital in February 2011 and October 2018, respectively. The gastric conduit was created using a hand-assisted laparoscopic or open laparotomy technique. Cervical esophagogastric anastomosis was performed by end-to-side circular stapler anastomosis or by end-to-end anastomosis with handsewn double-layered running or interrupted absorbable sutures. All patients received routine tube feeding via jejunostomy.

Definitions of postoperative complications. The principal outcome was the development of postoperative infectious complications in the 30 days following surgery. In accordance with previous reports, we defined postoperative infectious complications as infections that revealed signs, symptoms, changed laboratory data, and/or imaging evidence, such as fever (>38.0˚C), elevated white blood cell count (≥12,000/mm³), or computed tomography (CT) imaging indicating new or progressive infiltration (10). The severity of postoperative complications was graded according to the Clavien–Dindo (CD) classification system (11). Complications were defined as items that were CD grade II or higher. The infectious complications recorded included anastomotic leakage, pneumonia, surgical site infections, pyothorax, cholangitis, peripheral phlebitis. Anastomotic leak was defined as a disruption of esophagogastric anastomosis and was diagnosed clinically or based on imaging findings (radiographic contrast study or CT scans). Clinical leak was defined as the appearance of saliva, luminal contents, or pus through the wound site with local inflammation, fever, or leukocytosis (12). All patients underwent a routine radiologic contrast study using thin barium on the seventh postoperative day. Radiologic leak was defined as contrast extravasation during the contrast study. Pneumonia was diagnosed based on the definition of pneumonia from the American Thoracic Society and Infectious Diseases Society of America (13). Evaluation and definition of surgical site infections (SSIs), including superficial incisional, deep incisional, organ, or space SSI, were assessed based on clinical diagnosis of healthcare-associated infection as defined by the US Centers for Disease Control and Prevention (CDC) (14). Pyothorax was defined as fluid in the pleural space noted in CT imaging and confirmation of infection based on drainage fluid culture (15). Acalculous cholecystitis was defined as acute inflammation of the gallbladder in the absence of gallstones with symptoms of fever together with blood tests showing elevated white blood cell count and hepatobiliary enzyme level (16). Peripheral phlebitis was defined as localized irritation or inflammation of the vein wall with a combination of fever, tenderness/pain, and erythema (17). All postoperative complications were classified based on the basic complications list of the Esophageal Complications Consensus Group.

Assessment of skeletal muscle mass and sarcopenia. CT images before and after NAC were obtained to assess skeletal muscle mass. Muscle cross-sectional area is linearly related to whole-body muscle mass (18). Skeletal muscle was evaluated using CT attenuation values with thresholds ranging from -30 to 150 Hounsfield units. A Synapse Vincent 3 image analysis system (Fujifilm Medical, Tokyo, Japan) was used to measure the cross-sectional area of skeletal muscle in the L3 region (psoas, paraspinal, and abdominal wall muscles) using abdominal CT. To standardize according to patient height, skeletal muscle mass index (SMI) (cm²/m²) was calculated by dividing the total skeletal muscle area (cm²) at the L3 level by the square of height (m²) (19). Pre- and post-NAC SMI were calculated, and SMI change before and after NAC was expressed as % skeletal muscle loss (%SML). Sarcopenia was defined as L3 SMI ≤40.8 cm²/m² for men and 34.9 cm²/m² for women (20).

Data collection. The following information was collected and analyzed: sex, age, American Society of Anesthesiologists physical status (ASA-PS) classification, tumor location, histology, and clinical tumor node metastasis classification. The following parameters were measured before and after NAC: albumin (Alb) level (g/l), white blood cell count (10⁹/l), neutrophil count (10⁹/l), lymphocyte count (10⁹/l), platelet count (10⁹/l), carbohydrate antigen 19-9 level (U/ml), and carcinoembryonic antigen level (ng/ml). Tumor node metastasis (TNM) criteria from the eighth edition of the Union for International Cancer Control classification system were used for tumor staging (21). To evaluate nutritional and immune-inflammatory statuses, we used prognostic nutritional index (PNI), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR). PNI reflects the nutritional status of patients with cancer and is predictive of survival and postoperative complications (22). NLR and PLR are surrogate markers of inflammation and immunological status and are reliable predictors of postoperative complications and response to NAC (23). PNI was calculated using the following equation: serum Alb level (g/l) + 5 × total lymphocyte count (10⁹/l). NLR was calculated as total neutrophil count (10⁹/l) divided by total lymphocyte count (10⁹/l). PLR was calculated as total platelet count (10⁹/l) divided by total lymphocyte count (10⁹/l).

Statistical analysis. Continuous and categorical variables are summarized by frequency (percentage) and mean±standard deviation. To compare the two groups, the Fisher exact test and the chi-squared test were used for categorical variables, and the Student’s t-test was used for continuous variables. Logistic regression analysis was used to evaluate the association among predictive factor candidates and postoperative infectious complications, with odds ratio, 95% confidence interval, and p-values based on the Wald test. To avoid multi-collinearity in the multivariable regression model, only one factor among two variables, which had a Spearman’s correlation coefficient >0.4, was selected as a predictor candidate. Factors with p<0.10 on the univariable analysis were included in the multivariable logistic regression model. A p-value<0.05 was considered statistically significant. Statistical analyses were performed using EZR software (Saitama Medical Center, Jichi Medical University, Japan) (24).

Patient characteristics. The characteristics of the 123 patients included in the study are listed in Table I. The median age was 63 years (range=52-82 years). Tumors were located in the upper thoracic esophagus in 18 patients (14.6%), in the middle thoracic esophagus in 48 (26.6%), in the lower thoracic esophagus in 50 (39%), and in the esophagogastric junction in 7 (5.6%). Ninety-one patients (73.9%) completed two courses of NAC. There was no correlation between any variable and incidence of postoperative infectious complications (Table I).

Postoperative infectious complications. Postoperative infectious complications occurred in 41 patients (33.3%). Complications categorized as CD grade II, III, IV, and V were observed in 27, 12, 2, and 0 patients, respectively. The most frequently occurring complication was pneumonia, observed in 13 patients. SSIs were the second most frequent complication, observed in 12 patients. Eight patients with SSIs had wound infections at the site of cervical incision caused by cervical chyle leakage, and four patients with SSIs were infected at the site of a placed enteral feeding tube. Ten patients suffered from superficial SSIs. Anastomotic leakage was observed in 10 patients (Table II).

Indicators of nutritional and immune-inflammatory status and skeletal muscle mass. Forty-five patients (36.6%) had sarcopenia before NAC, increasing to 52 (42.3%) after NAC. A reduction in SMI was observed in 105 patients (87.8%) during NAC. The % SMI loss was significantly greater in patients with postoperative complications than in those without complications. No significant differences were found in the other parameters, including Alb, PNI, NLR, PLR, body mass index, and SMI before and after NAC (Table III).

Univariable and multivariable analysis of risk factors for postoperative complications. Potential predictive factors for postoperative infectious complications were evaluated using univariable and multivariable analyses. In multivariable analysis, % SMI loss (OR=0.89; 95%CI=0.79-0.99; p=0.048) was independently associated with infectious complications (Table IV).

The findings of this study indicate that skeletal muscle loss during NAC is an independent predictor of postoperative infectious complications. It is important to note that all patients in this study received the Japanese standard of CF preoperative chemotherapy. While this regimen is not typically used in Western countries, similar therapies are often used; therefore, our finding of skeletal muscle loss due to neoadjuvant therapy has important implications for both medical communities.

The key finding of this study is that skeletal muscle loss during NAC was an independent predictor of postoperative infectious complications. One possible explanation for this is that excessive skeletal muscle loss leads to frailty and impaired immune function. It has been reported that skeletal muscle functions as a secretory organ that produces a variety of inflammatory and anti-inflammatory cytokines and other peptides (25,26). Deterioration of immune function accompanied by excessive skeletal muscle loss may increase the risk of postoperative infectious complications. Furthermore, it is well recognized that proteins and amino acids are essential for wound healing, and that specific amino acids promote immune cell function (27). Thus, it is possible that a rapid deterioration in the metabolism of a variety of amino acids, such as leucine, glutamine, and arginine, during the progression of sarcopenia may have caused the anastomosis leakage and SSIs found in this study.

Contrary to common perception, our study failed to show a predictive value for nutritional parameters for postoperative infectious complications, including PNI and Alb before and after NAC. This may be due to variation in serum Alb levels. It has been demonstrated that Alb levels decline with age at a rate of 0.08-0.17 g/l per year, and that this decline is faster in males than in females (28). The patients in our study were mainly male, and there were wide ranges in age and Alb levels (age, 52-82 years; pre-NAC Alb, 2.6-4.8 g/l; preoperative Alb, 1.4-4.5 g/l). As for inflammatory indices, NLR and PLR were not predictors of postoperative infectious complications in this study. One possible reason for this is that immunosuppression and inflammation were not significantly affected by NAC with two courses of CF. Several studies have reported that, when the circulating lymphocyte count is decreased due to neoadjuvant chemotherapy with docetaxel, the concurrent use of CF or CRT causes immunological suppression and excessive inflammatory response, leading to severe postoperative complications (29,30). However, our study population only included patients undergoing NAC with CF, which induced a relatively small reduction in lymphocyte count compared to other neoadjuvant therapies, including docetaxel plus CF or CRT (31). Recently, other useful inflammatory indices, such as albumin-bilirubin status and platelet-to-albumin ratio were reported (32,33). These new indicators may also be worth evaluating.

Although the nutritional and immunological parameters assessed in the present study were not predictors of postoperative complications, understanding the inflammation status and nutritional condition of patients is still of great importance, as it is well known that there is interaction between excessive inflammation, nutrition deficiency, and sarcopenia in cancer patients (34,35). Recently, several studies have reported the beneficial effects of nutritional management and the implementation of physical therapy for patients with sarcopenia before surgery (36). However, the practicality of nutritional and exercise regimens for patients with cancer has not yet been established. Further studies are needed to explore appropriate exercise and nutritional protocols in relation to type of surgical stress and patient condition, especially under neoadjuvant treatment.

There are some limitations to this study. First, it is a retrospective study conducted at a single institution that included a relatively small number of patients, and it did not include the dose intensity of NAC or related adverse events; thus, the reasons for the failure of NAC were not evaluated. Second, it relied on CT images alone for the assessment of sarcopenia. Further study is needed based on a more comprehensive evaluation of sarcopenia using well-established indicators of skeletal muscle status, such as handgrip strength, bioelectrical impedance analysis, and dual-energy X-ray absorptiometry.

In conclusion, this study suggests that skeletal muscle loss during NAC predicts postoperative complications. Patient outcomes may be improved by the optimization of pre-treatment skeletal muscle volume and the prevention of skeletal muscle loss during cancer treatment.

The Authors have no conflicts of interest to declare in relation to this study.

Study conception and design: Kazuya Higashizono and Shinsuke Sato. Acquisition of data: Kazuya Higashizono, Masato Nishida, and Shinsuke Sato. Data analysis and interpretation: Kazuya Higashizono, Shinsuke Sato, and Eiji Nakatani. Drafting of the manuscript: Kazuya Higashizono, Philip Hawke, and Shinsuke Sato. Critical revision of the manuscript: Eiji Nakatani, Erina Nagai, Yusuke Taki, Masato Nishida, Masaya Watanabe, and Noriyuki Oba.

The Authors thank the Medical Research Support Project of the Shizuoka Prefectural Hospital Organization for its support.

This work was aided by the Medical Research Support Project of Shizuoka Prefectural Hospital Organization.