To our knowledge, ACs are tumors located at the junction of the distal bile duct, the main pancreatic duct and the duodenum. They are usually classified into pancreaticobiliary, intestinal and mixed tumors, by which some clinicopathological scores and nomograms have been established to evaluate prognosis3,16,17. However, these predicting models were not sufficient to evaluate the outcome of patients with AC. Therefore, some researchers thought that it would be more beneficial to include some biomarkers such as CK7, MUC1 and MUC5AC; however, this was controversial with regard to the prognostic value of the molecular alterations18,19,20. Moreover, too many prognostic factors would be needed to construct a significant model. Therefore, up to now, there is still no effective and suitable model for predicting prognosis. In our study, 2341 patients were extracted from the SEER database to investigate the prognostic factors of CSS. As for the basic characteristics of AC, consistent with other studies, we found that the age at diagnosis of patients with AC mainly ranged from 50–70 years, white people accounted for a majority of the patients and most of the tumors were smaller than 5 cm21,22. As for the LNM rate, we found that it was almost as high as the no LNM rate. Actually, it has been reported that the LNM rate of AC is high. John R et al. reported that positive LNM could be found in 45% of T1 patients and 86% of T4 patients22.
As for the curative treatment of AC, it is estimated that more than 80% of ACs are amenable to resection including surgical and endoscopic removal. For LNM negative lesions, pancreaticoduodenectomy was an indeed curative treatment, while it had a better ability to provide indications for surgery for LNM positive lesions although some lesions were in the early stage23. In spite of some notions about the invasion of lymphatic vessels, LNM was an important factor for the determination of treatment methods and to predict prognosis24. Hence, the number of harvested LNs was the key factor to determine the optimal LNM state. In our study, we identified the best cut-off value by the KAPS algorithm which has been used in many studies14,25. In consistence with some studies8,11, we found that patients with > 12 examined LNs have more benefit than those who with < 12; however, some studies thought the harvested LNs should be > 176,7. In addition, the multivariate logistic regression analysis showed that tumor size and T stage were independent factors of harvesting LNs, in corroboration with the results of a previous study26. With respect to N stage, some studies proposed that the best cutoff point for positive LNs was 0 and 310,27, while few studies thought that positive LNs should be divided into 0–1 and ≥ 2 groups7. In our study, the new LNM stage we proposed was N0 (0 positive LNs), N1 (1–4 positive LNs) and N2 (≥ 5 positive LNs), which made a great difference for survival. However, the positive LNs factor was not included in the construction of the nomogram plot because the value of AIC was too large. AIC was considered as an important criterion for variable sieving and has been used in many studies28,29. Compared with our model, the TNM staging system earlier was not better for survival prediction, while our model was reasonable and logic by multivariate cox regression analysis and AIC algorithm which can prevent over fitting of the model and ensure the accuracy of model30. In our model, we recruited age, T stage, M stage, pathology grade and examined lymph nodes other than TNM stage, avoiding the insufficiency of TNM stage. Naturally, nomogram we conducted performed better than TNM stage, which was demonstrated by ROC curve and DCA analysis.
Our study had some limitations that should be discussed. First, the TNM staging used was the 7th edition rather than the 8th edition, which may influence the results of the comparison between the nomogram and TNM staging models. Hence, it is necessary to perform studies to compare the model constructed by our study with the 8th edition of TNM staging. Second, we excluded many patients who had missing data associated with our collected variables, increasing the selection bias. Third, the variables including examined LNs and positive LNs were diagnosed depending on each doctor in different clinical centers. Finally, the enrolled prognostic parameters were so limited that we could not comprehensively analyze them. Therefore, although this nomogram performed well in the two cohorts, it should be applied with great caution when assessing the risk of 1-, 3- and 5- year survivals. In the future, we will collect our relevant data to incorporate the factors above into further research.
In conclusion, the present study was constructed to investigate the optimal examined and positive LNs. We found that the examined LNs factor was beneficial for the prognosis of the patients, which was more favorable with at least 12 LNs. We also modified the current N staging into three groups based on number of metastatic LNs: N0, no LN metastasis; N1, 1–4 metastatic LNs; and N2, ≥ 5 metastatic LNs. Based on the categories and multivariate analysis, we developed and validated a nomogram with greater benefit for predicting the survival of patients with AC than the TNM staging, which was demonstrated by td-ROC and DCA.