Incidence, clinical features, and survival outcomes of primary malignant conjunctival tumor: a US population-based retrospective cohort analysis based on the SEER database (1975-2018).

Primary malignant conjunctival tumors (PMCT) are rare. Their clinicopathological characteristics and survival outcomes are not well understood. The Surveillance, Epidemiology, and End Results (SEER) database includes approximately 30% of the total US. In this study, we aimed to investigate the epidemiology, clinical characteristics, and prognosis of PMCT via SEER. Data on microscopically confirmed PMCT patients from 1975 to 2018 were retrieved. Patients who were lost to active follow-up, those for whom PMCT was not the primary malignant tumor, and those with unknown death information, laterality, race, or those who survived for less than 1 month after diagnosis were excluded. Disease-specific survival (DSS) and overall survival (OS) were the primary endpoints, calculated through the Kaplan-Meier analysis and log-rank tests. Univariate and multivariate Cox regression analyses were conducted to recognize independent predictive factors for DSS and OS. In total, we identified 2,853 eligible patients diagnosed with PMCT, with an average age of 61.25 years, among which 1,678 (58.82%) were males, 2,464 (86.37%) were whites, 1,567 (54.92%) were married, and 2,125 (74.48%) were in localized SEER stage. The three major types were lymphoma (39.64%), squamous cell carcinoma (SCC) (34.88%), and melanoma (21.98%). The overall incidence of PMCT was 0.136/100,000 between 1975 and 2020, with an annual incidence rate of 0.929 [95% confidence interval (CI): 0.289-1.573, P<0.05]. Multivariate Cox regression analysis discovered age, sex, marital status, histological type, SEER stage, and surgery as independent prognostic variables. Age ≥75 years [≥75 vs. <60 years, hazard ratio (HR) =3.211, 95% CI: 2.309-4.466, P<0.001], melanoma (melanoma vs. SCC, HR =4.637, 95% CI: 3.235-6.649, P<0.001), distant SEER stage (distant vs. localized, HR =4.318, 95% CI: 2.675-6.968, P<0.001), and no/unknown surgery status (performed vs. no/unknown, HR =1.565, 95% CI: 1.187-2.062, P=0.001) were related to worse DSS. Meanwhile, age ≥75 years (≥75 vs. <60 years, HR =9.399, 95% CI: 7.876-11.216, P<0.001), male (female vs. male, HR =0.701, 95% CI: 0.612-0.803, P<0.001), unmarried status (unmarried vs. married, HR =1.342, 95% CI: 1.17-1.538, P<0.001), distant SEER stage (distant vs. localized, HR =2.077, 95% CI: 1.498-2.881, P<0.001), and no/unknown surgery status (performed vs. no/unknown, HR =1.16, 95% CI: 1.018-1.322, P=0.03) were related to worse OS. Lymphoma (lymphoma vs. SCC, HR =0.628, 95% CI: 0.533-0.74, P<0.001) was associated with better OS. PMCT incidence increased after 1975 and decreased after 1997. Age, histological type, SEER stage, and surgery were all significantly associated with DSS and OS. Age ≥75 years, melanoma, and distant SEER stage were associated with worse DSS, while age ≥75 years, male, unmarried status, distant SEER stage were related to worse OS and lymphoma was related to better OS. Surgery may improve the prognosis of patient with PMCT.