Characteristics of patients
A total of 1,956 patients who met the inclusion criteria and had complete information were identified from the SEER database. Table 1 shows the baseline demographic and clinicopathological characteristics. The median age of all patients was 60 years (range, 21–95). More than half of the patients were diagnosed at 60 years of age and older. The majority of the patients were White (89.2%), women (66.6%) and TC (87.0%). The most common primary sites were lower lobe (40.5%) and upper lobe (31.7%). More than half of the laterality was right (58.4%). The most frequent primary tumor size was between 20 and 40 mm (44.6%), followed by tumor size < 20 mm (43.0%). In all, 74.2% of patients had well-differentiated tumors and 71.0% of patients were categorized with localized disease. Among atypical patients, 25.6% of patients had well-differentiated tumors and 46.1% of patients were categorized with localized disease. Regarding treatment, 88.5% of patients were managed by surgery, only 5.6% received radiation treatment, and only 5.8% received chemotherapy treatment. Of the patients who were treated with surgery, 63.1% had a lobectomy resection, whereas 13.5% had wedge resection.
Prognostic factors of CSS
The univariate and multivariate results of prognostic factors for CSS of patients with lung carcinoid tumors are shown in the Table 2. In univariable analyses, statistically significant predictive factors of CSS included age at diagnosis (P < 0.001), insurance (P = 0.002), grade (P < 0.001), historic stage (P < 0.001), histological type (P < 0.001), T Stage (P < 0.001), N stage (P < 0.001), M stage (P < 0.001), surgery of primary site (P < 0.001), radiation of primary site (P < 0.001), chemotherapy treatment (P < 0.001), radiation after surgery (P < 0.001), and tumor size (P < 0.001). Multivariate analyses only included these prognostic factors with statistical significance in the univariate models. Younger age at diagnosis (P < 0.001), having insurance (P = 0.001), well-differentiated tumor (P < 0.001), TC (P = 0.001), N0 stage (P = 0.039), M0 stage (P = 0.013), and no radiation therapy (P = 0.040) were significantly associated with improved CSS among patients with lung carcinoid tumors. Received lobectomy resection (P < 0.001), local resection (P = 0.010), or pneumonectomy resection (P = 0.001) were also significantly associated with improved CSS. Tumor size between 20 and 40 mm (P = 0.023), or larger than 40 mm (P < 0.001) were negatively associated with CSS among patients with lung carcinoid tumors.
Prognostic factors with CSS in subgroup of histological type
We also evaluated prognostic factors in a separate histological type of lung carcinoid tumors (Table 3). Among patients with TC, younger age at diagnosis (P < 0.001), female (P = 0.039), having insurance (P = 0.049), well-differentiated tumor (P < 0.001), resection surgery of the primary site (lobectomy resection/wedge resection/pneumonectomy, all P < 0.05), no chemotherapy (P = 0.020), and tumor size < 20 mm (P < 0.000) were independent prognostic factors, and positively associated with improved CSS. In contrast to TC, only younger age at diagnosis (P = 0.031), M0 (P < 0.000), lobectomy resection (P = 0.002), and tumor size < 20 mm (P = 0.031) were associated with CSS among patients with AC.
Nomogram development and validation
Figure 1 shows the nomogram for predicting CSS of lung carcinoid tumors using the significant independent factors that were found in the multivariate analysis. The nomogram showed that the largest contributions to prognosis were resection surgery of primary site and tumor size of primary site, followed by M stage. The C-index for the CSS predictive nomogram was 0.873 and confirmed to be 0.861 through bootstrapping validation. The features of calibration plots for CSS probability at 3, 5, and 10 years indicated that the concordance between predicted and observed survival was optimal (Fig. 2a–c). Furthermore, DCA demonstrated great positive net benefits in the predictive model among nearly all of the threshold probabilities at different time points, which prove the potential clinical values of this model (Fig. 2d). The area under the curve of the nomogram for predicting the CSS rate of lung carcinoid tumors was 0.868, which exhibited superior survival predictive ability of the nomogram model (Fig. 2e).
Kaplan-Meier analyses
With a median (range) follow-up of 126.5 (10–364) months, Kaplan-Meier analysis revealed that the median CSS was not reached. As shown in Figure 3, worse CSS for patients with lung carcinoid tumors was shown in patients of advanced age (≥60 years), lacking insurance, moderately, poorly, or undifferentiated tumor, AC, N1–N3 stage, M1 stage, radiation therapy, not receiving surgery treatment, and large tumor size (20–40 mm and >40 mm).