A nomogram to predict the prognosis of patients with unresected rectal adenocarcinoma undergoing chemoradiotherapy: a population-based study

Background: Chemotherapy combined with radiotherapy is the main treatment strategy for unresectable rectal cancer. However, the prognostic factors of patients with unresectable rectal cancer treated with radiotherapy and chemotherapy have not been systematically studied. Therefore, this study investigated the prognostic factors and prognosis based on surveillance, epidemiology and final results of the SEER medical insurance database. Methods: Primary rectum patients were selected from the SEER database. The independent prognostic factors associated with overall survival (OS), cancer-specific survival (CSS) and noncancer-related death were evaluated using the Kaplan-Meier method and log-rank test, a competing risk model, and the Cox proportional hazards regression model. Two nomograms were established for predicting the 1- and 3-year OS and CSS of patients. Results: A total of 3,998 rectal adenocarcinoma cancer patients who received chemoradiotherapy but had not undergone surgery were included in this study and divided into training (n = 3559) and validation cohorts (n = 439). Patients in the training cohort had a 1-year OS rate of 65.7±0.8%, a 3-year OS rate of 26.6±0.8%, a 5-year OS rate of 1.6±0.8%, and a median survival rate of 20.0 months (range, 19.22-20.8 months). The following factors were significant prognostic factors of OS: age (p< 0.001); tumour grade (p< 0.001); T stage (p< 0.001); M stage (p< 0.001); bone metastasis (p<0.001); brain metastases (p<0.001); liver metastases (p<0.001); lung metastases (p<0.001); marital status (p<0.001) and insurance status (p=0.005). Age (p< 0.001), tumour grade (p< 0.001), T stage (p< 0.001), M stage (p< 0.001), bone metastasis (p<0.001), brain metastases (p<0.001), liver metastases (p<0.001), lung metastases (p<0.001) and race (p=0.034) were independent prognostic factors of CSS. Age (p< 0.001), T stage (p< 0.001), N stage (p=0.007), M stage (p<0.001), liver metastases (p<0.001), lung metastases (p<0.001), marital status (p<0.001) and insurance status (p=0.019) were independently associated with noncancer-related death. Conclusion: Age, tumour grade, T and M stage, bone, brain, liver and lung metastases, marital status and insurance status are independent risk factors for the OS of rectal adenocarcinoma patients who have undergone chemoradiotherapy but have not undergone surgery. Age, tumour grade, T stage, M stage, bone, brain, liver, lung metastases and race were independent prognostic factors of CSS. Age, T, N and M stage, liver and lung metastases, marital status and insurance status, were independently associated with noncancer-related death. Interestingly, the earlier the T stage was, the higher the rate of noncancer-related death. Two nomograms were developed to predict OS and CSS, and the C-indexes were 0.6776 and 0.6744, respectively. Rectal cancer screening is strongly recommended for patients under the age of 50.