A neotype nomogram based on accessible clinical indicators to predict the overall survival of esophageal cancer patients underwent radical resection


 Background: Esophageal cancer (EC) is a malignant tumor with dreadful mortality, nomogram is a prognosis tool of great significance in therapeutic guidance and assessment. We aimed to establish a newly-built nomogram for OS prediction of EC patients with radical esophagectomy.Methods: A total of 311 EC patients underwent radical esophagectomy were retrospectively investigated with their survival and demographic and clinicopathological data. Patients were randomly divided into the primary and validation cohorts. The establishment of nomogram was based on Cox hazard regression analysis in primary cohort, the calibration curves and Harrell’s concordance index were performed to verify the predictive accuracy while ROC curves was adopted to reflect the efficacy of nomogram. Kaplan–Meier curves showed the clinical significance of risk classification system and Pearson correlation test was utilized to show the correlation between risk classification system and TNM staging.Results: The median OS and 5-year survival rate are 44 months and 29.8% in primary cohort. In validation cohort, they are 52 months and 27.1%, respectively. In Cox hazard regression analysis, we extracted six independent prognostic factors—age, gender, AGR, PRL, N stage, PNI—to establish the nomogram. The C-index of nomogram is 0.75 in primary cohort and 0.70 in validation cohort. Calibration curves indicated high consistency between accurate and predicted OS in both primary and validation cohorts. ROC curves showed a better efficacy of nomogram compared with AJCC T and N stage. The area under curve (AUC) of primary cohort is 0.801 and 0.727 in validation cohort. Patients in primary cohort were divided into three risk groups according to the nomogram score, the median OS between each group was significantly different. Analogical results were obtained in validation cohort. Furthermore, the risk classification system was strongly correlated to AJCC TNM staging system in total cohort (r2=0.647, P<0.001), and it also demonstrated a better OS prediction efficacy (AUC=0.742).Conclusions: We established a neotype nomogram and a relevant risk classification system with verified accuracy and efficacy in OS prediction of EC patients after radical esophagectomy. They may provide feasible value in prognosis assessment and treatment guidance prospectively.


Background
As a malignancy with ascending morbidity and mortality worldwide, esophageal cancer (EC) seriously threatens human life and health.(1) Additionally, as a result of diet and living habits, esophageal cancer ranks as the 6th incidence of malignancy, and the mortality rate of which ranks 4th in China. (2) The most common pathological type of esophageal cancer is squamous cell carcinoma in China while in western nations, it is adenocarcinoma. Radical resection is the major therapy for esophageal cancer. However, due to lack of accurate early diagnosis approaches and effective prognostic indicators, the 5-year overall survival (OS) rate of EC is around 30%. (3) Recently with the evolution of neoadjuvant chemoradiotherapy, the prognosis of radical esophageal cancer surgery has been markedly improved.(4) Particularly, an accurate evaluation of EC patient prognosis contributes to formulating more precise and individualized treatment strategies to prolong survival.
Various factors have a crucial in uence on the prognosis of EC patients especially the survival rate which described as independent prognostic factor. With decades of widespread multi-center clinical research, tumor-node-metastasis staging system represented by American Joint Committee on Cancer (AJCC TNM) as well as age, pathological type, treatment patterns are approved as conventional independent prognostic indicators for EC. (5) However, due to the confounding factors that affect the prognosis of EC, single-handed AJCC staging cannot predict the prognosis satisfactorily, especially for patients with the similar staging. (6,7) Nomograms are widely utilized in cancer prognosis for their ability to transform statistical prediction results into a comprehensive quantitative and visual estimate of the probability of an event, such as death or recurrence. (8,9) As a malignancy with poor prognosis and survival, nomogram studies related to EC survival and recurrence are of gigantic signi cance. The establishment of nomograms integrating conventional factors for EC has been noted in a few studies. (10)(11)(12) Furthermore, a series of indicators that can be converted by routine clinical examination parameters have been found to show considerable prognostic potential in EC patients such as albumin to globulin ratio (AGR), neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), Prognostic Nutritional Index (PNI), Low-density lipoprotein (LDL). (13)(14)(15)(16) However, few studies on the nomogram combining these certi ed novel prognostic factors in EC are published.
In this study, we aim to retrospectively investigate the independent prognostic factors for OS in EC patients underwent radical esophagectomy and establish an applicable nomogram for internal and external validation and exploring its prediction e cacy compared with AJCC staging.

Patients
The clinicopathological and survival data of 311 patients underwent radical resection of esophageal cancer during 2008 and 2013 in The First A liated Hospital of Zhejiang University School of Medicine were retrospectively collected and analyzed. The following are the inclusion criteria: (1) patients with a con rmed pathological diagnosis of EC (squamous or adenous) in rst admission; (2) patients without any anti-tumor therapy before surgical esophagectomy; (3) the data of patients are completed. The exclusion criteria followed: (1) patients with a pathology type other than adenocarcinoma or squamous cell carcinoma; (2)  The variables of each patients included demographic data: age, gender, smoke and alcohol status, BMI; clinicopathological data: CEA (ng/ml), tumor location, differentiated degree, T and N stage, LDL (mmol/L); available prognostic indicator: AGR, NLR, PLR, PRL, PNI. All baseline data were obtained in a week before radical esophagectomy.
A. BMI (Body mass index) = Body weight (kg)/ (Height (m) ^2). B. T and N stage: According to the 7th edition AJCC TNM staging guideline of EC.
C. AGR: Albumin to globulin ratio.

Statistical Methods
Categorical variables were classi ed based on clinical ndings, and continuous variables were transformed into categorical variables based on cut-off points determined by median values or recognized clinical ndings. In the balance control between primary and validation cohorts, chi-square was utilized to show the difference of proportion in each variable.
In primary cohort, univariable and multivariable Cox's proportional hazards regression for OS was performed, and variables with P values less than 0.05 in the multivariable Cox's proportional hazards regression were utilized to establish a predictive nomogram model. (8) The predictive accuracy of the nomogram model was performed using the Harrell's concordance index (Cindex) and calibration curves, the larger value of C-index indicated more e cient ability to correctly discriminate the prediction of outcome. (19) Calibration curves for 1-year, 3-year, 5-year OS were performed using a bootstrap method to quantify the modeling strategy of nomogram. Receiving operative characteristics (ROC) curves were used to compare the prediction e cacy of nomogram with AJCC staging. All the methods above were equally implemented in validation cohorts for external veri cation.
Furthermore, based on the total score from the predictive nomogram model, patients were divided into 3 risk groups (low risk, intermediate risk, high risk) in both primary and validation cohorts. Kaplan-Meier curves and the log-rank test were used to illustrate and compare the OS of patients in the different risk groups.
In the total cohort, chi-square and Pearson correlation test were applied to show the correlation between risk classi cation system and AJCC TNM staging system.
All the statistical analyses and graphics above were performed using the SPSS 25.0 statistical package (SPSS Inc., Chicago, IL, USA) and R version 3. 6 Table 4 showed the risk classi cation was strongly correlated to AJCC TNM stages (r 2 = 0.647, P < 0.001). Additionally, Kaplan-Meier curves in Fig. 6A showed signi cant difference in OS of patients between risk classi cation and TNM stages (log-rank: P < 0.001), and a larger AUC of risk classi cation system than TNM stages (0.744 vs. 0.699) was displayed in Fig. 6B.

Discussion
The prognostic factors in EC patients are known to be complicated, thus, an accurate and comprehensive prognostic method is of great signi cance for the evaluation of esophageal cancer and the optimization of treatment strategies. So far, TNM staging system proposed by AJCC has been widely accepted for the assessment of cancers including EC. For patients who are adapted to surgery, determining explicit T and N staging is the most crucial task throughout. (20) However, the TNM staging system mainly represents anatomical relevance, sometimes does not fully re ect the prognosis. Therefore, a type of model called nomogram that can incorporate multiple prognostic factors is maturing. Recently, nomograms are popularly investigated in cancer-related survival, recurrence and metastasis with considerable potential. For demographic characteristics, we found that two factors, age and gender, were associated with OS of EC patients after radical esophagectomy, and thus were included into the establishment of nomogram.
As a matter of genetic difference, males have been found with higher incidence and mortality in a variety of malignancies, as found in various studies and con rmed in ours. (1,27,28) In addition to cancerrelated factors, it cannot be ignored in the prognosis of elderly cancer patients that the pathological mechanisms induced by aging may cause more nutritional and metabolic diseases and disorders such as amyotrophy, metabolism damage and neurological disease, contributing to the impediment of longevity. (29)(30)(31) In the result of our study, the age over 65 years old was certi ed as an independent factor for OS prediction, conforming to the interpretation mentioned above.
Further in comparison with some nomogram studies in resectable EC patients, Shao's study focuses on the predictive ability of in ammation-related factors for OS, and accordingly building a nomogram model. His study is partially similar to our study, and some factors, including PLR and NLR, are selected to be used in our initial analysis.(32) However, with no statistical difference found, they were removed from multivariable Cox hazard regression analysis in our study. The above situation indicates that the factors affecting the OS of radical resection EC patients are very complicated. PLR and NLR are not only related to the prognosis of malignant tumors, but also determined in in ammatory diseases such as Rheumatic Disease and cardiovascular diseases. (33,34) EC is dependent on the complex interaction between the tumor and the hosts' in ammatory response, so the distinction of PLR and NLR shown between Shao's study and ours imply that the independence of factors affecting prognosis are unseparated from the integrity of the individual physiology.(35) As aforementioned, a low AGR is associated with increased cancer mortality in cancer patients, a generally healthy screened population study proves AGR as a risk factor for cancer incidence and mortality, in both short-and long-term cohorts. (36) There is biological plausibility for the link between low AGR and increased cancer incidence and mortality that an increase of cytokines on account of tumor microenvironment may elevate the total protein levels with induced albumin synthesis suppression in the liver.(37, 38) As for EC patients, a malnutrition status relevant decreased serum albumin and AGR level could be another mechanism of poor survival. PNI is composed of serum albumin level and lymphocyte count as a calculative index which is widely utilized for prognostic evaluation of various malignancies. As a factor re ects to tumor-related nutritional status and system in ammation response, the role of PNI in EC patients' prognosis is highly desirable for study.
Kazuo's study demonstrated the predictive role of PNI in EC patients outcome and its inseparable relationship with Tumor-in ltrating lymphocytes (TILs).(15) As proved, PNI was signi cantly associated with OS in Cox hazard regression analysis with a negative correlation of HR 0.676 (95%CI: 0.463-0.987) in our study, and it's rstly included in the nomogram for OS prediction in resectable EC patients.
Moreover, the laboratory-sourced factors we selected are all preoperative to eliminate the in ammatory and metabolic bias caused by surgery.
For resectable EC patients, though there is a gap in skills between surgeons, the lymph node dissection degree is considered as an effective adjudication, extended lymph node dissection proves a signi cant amelioration on the prognosis of EC patients. (39,40) Recently, the ratio of positive retrieved lymph nodes to total number of retrieved lymph nodes-known as the positive lymph node ratio (abbreviation as PRL or LNR)-has been shown to be a superior indicator of survival in EC. (41,42) Compared with N stage according to AJCC, it not only re ects the quantity but the extent of the lymphatic metastasis, especially for the EC patients with less than two-eld lymph node dissection or underestimated N staging due to In the end, we performed analysis based on the risk classi cation system in total cohort, comparing with an authoritative tumor staging system AJCC TNM staging to identify its comprehensive application clinically. Eventually, the risk classi cation system showed strong correlation with TNM staging (r 2 = 0.647, P < 0.001), and a better e cacy in OS prediction than TNM staging was informed by log-rank test and ROC curves.
In contrast with studies on nomogram in EC patients, PNI, which is scarcely investigated in nomogram of EC patients, was integrated into our study, together with internal and external validation of nomogram.
Besides, an applicable risk classi cation system based on nomogram is developed in our study. (11,16,32) Several limitations exist in our study. Firstly, it's a retrospective analysis with probably inherent bias.
Secondly, the primary and validation cohorts of this study are from a single center. Thirdly, the threshold index of factors mentioned in our study is heterogeneous. Therefore, a large-sample, multi-center randomized trial needs to be further veri ed.

Conclusions
We established and veri ed a nomogram composed of six clinically accessible factors including a corresponding risk classi cation system for OS prediction in EC patients underwent radical esophagectomy. The nomogram showed considerable accuracy and e cacy compared with conventional AJCC staging system. The results can be applied to instruct prospective clinical applications, such as patient counseling, prognosis assessment and individualized therapeutic decisionmaking.

Declarations
Ethics approval and consent to participate  Figure 1 A ow chart for the design of our study. A total of 311 EC patients underwent radical esophagectomy were randomly divided into primary and validation cohorts. A nomogram was built based on the primary cohort, the accuracy and e cacy of the nomogram and relevant risk classi cation system were veri ed in both primary and validation cohort. Finally, the clinical assessment of risk classi cation system was performed in total patients. EC: Esophageal cancer. Nomogram prediction model for OS of EC patients underwent radical esophagectomy. As showed above, six variables correspond to the upper points scale respectively, while the sum score of each variable reaches downward to the total points which is related to the prediction of 1-, 3-, 5-year overall survival rate. Moreover, a line bar composed of three colors indicates three risk group according to the predictive OS. Furthermore, the risk status of radical esophagectomy EC patients would be obtained based on the nomogram. AGR: albumin to globulin ratio, PRL: positive lymph nodes ratio, PNI: Prognostic Nutritional Index, N: modi ed N staging, Inter-risk: Intermediate risk.