Clinical characteristics and prognostic factors of anal adenocarcinoma: a nomogram development based on SEER database and validation in the WCH database

The purpose of this study was to comprehensively understand anal canal adenocarcinomas (AA) and develop a nomogram for prognostic prediction of AA. Data were extracted from the Surveillance, Epidemiology, and End Results (SEER) database (the year 2004–2015). An external validation set was collected from West China Hospital (WCH) databases. Propensity-score matching (PSM) was performed to balance the demographic characteristic. A novel nomogram was developed to estimate individual survival probability and its performance was validated using the concordance index (C-index), calibration curves, and decision curve analyses (DCA). A total of 7901 patients were enrolled including 749 AA patients and 7152 squamous cell carcinomas of the anal canal (ASCC) patients. Before PSM, patients with AA had shorter cancer-specific survival (CSS) and OS than those with ASCC. However, after PSM, patients with AA were related to a favorable OS (p < 0.001), but a comparable CSS (p = 0.140) to those with ASCC. Age, sex, grade, surgery, and M stage were the independent prognostic factors of CSS for AA and were included in the establishment of a novel nomogram. Patients from the WCH database (n = 112) were used as an external validation cohort. The C-index of the nomogram was 0.78 and 0.735 in internal and external validation, respectively, which suggested the good discrimination power of the model. Furthermore, calibration curves and DCA suggested good agreement between the predicted and actual survival. Lastly, a risk classification system based on a nomogram revealed the reliability of the novel model. AA and ASCC had distinct clinical features. AA was associated with a better prognosis than ASCC after PSM. The model of nomogram showed an accurate predictive ability for prognostic factors of AA patients.