Epidemiology of and prognostic factors for patients with sarcomatoid carcinoma: a large population-based study

Sarcomatoid carcinoma (SC) is regarded as a rare malignant neoplasm associated with poor outcomes. This study aimed to explore the epidemiological characteristics and prognostic factors of SC, and establish a clinical predictive model. The Surveillance, Epidemiology, and End Results database was used for data inquiry of patients with SC. Relevant population materials were used for age-adjusted incidence, limited-duration prevalence and prognostic analyses, and also for nomogram construction and validation. A total of 17,917 cases of SC were identified. Among them, 12,276 (68.52%) were women and 14,265 (79.62%) were white. Most cases occurred in the female genital system, accounting for 41.10% of all SCs. The median age at diagnosis was 68 years. The incidence and prevalence of SC increased substantially over time. The age-adjusted incidence increased from 0.31/100,000 in 1973 to 1.26/100,000 by 2014, a 4.06-fold change. Among site groups, the incidence of SC in the female genital and the respiratory system increased most significantly (P < 0.001). As for stage and grade, the incidence increased the most in distant and high-grade SC, respectively (P < 0.001). Moreover, the survival duration varied significantly by site, histology, stage and grade (P < 0.001). The multivariable analyses showed that the year of diagnosis, age, sex, race, grade, stage, and site were all significant prognostic factors (P < 0.001). Among these, stage and primary tumor site were the most valuable indicators of outcomes. Furthermore, a nomogram comprising age, histology, grade, stage and site were established to predict the 3-/5-year survival probability. The concordance indexes of the nomogram were 0.745 (95% confidence interval [CI]: 0.737-0.753) and 0.743 (95% CI: 0.728-0.756) for the internal and external validations, respectively. The calibration plot demonstrated satisfactory consistency between the actual and predicted outcomes in both the internal and external validations. In conclusion, increasing incidence and prevalence of SC was observed in our study, suggesting that SC is more prevalent than previously reported. Clinicians should be familiar with the characteristics of these tumors. Furthermore, the established nomogram could accurately predict the 3-/5-year survival rate of patients with SC, which may be of value for patient counselling and risk stratification.