Systemic mastocytosis: Statistics and impact of secondary malignancy on survival.

e22559 Background: Systemic mastocytosis (SM) is a rare disease characterized by clonal mast cell accumulation. The incidence of systemic mastocytosis is around 0.046 per 10,000 people in the United States. The symptoms stem from mast cell mediator release. While most cases are indolent, certain subtypes exhibit aggressive behavior. The diagnosis of systemic mastocytosis is made based on World Health Organization criteria. Treatment varies depending on disease severity, ranging from symptomatic management to chemotherapy, including the use of KIT inhibitors. Methods: Data was collected from Surveillance, Epidemiology and End Result database Research Plus Data, 17 Registries, Nov 2023 Sub (2000-2021), using the ICD Code 9741/3 for systemic mastocytosis. The analysis was stratified based on age, gender, race, year of diagnosis, primary site labelled, median household income, number of tumors and various treatment modalities. Survival curves were compared using the Log-Rank test (GraphPad Prism). Results: A total of 905 cases were identified, with a median age at diagnosis of 55 years, and 50.4% female. The racial distribution included 83.3% White, 9.4% Hispanic, 3.5% Black, 1.9% Asian/Pacific Islander, 1.3% of unknown race, and 0.55% American Indian/Alaskan. Among the patients, 28.3% had more than one malignancy. The 1-year overall survival (OS) was 0.889 (95% CI, 0.866–0.91), with a 3-year OS of 0.809 (95% CI, 0.78–0.834) and a 5-year OS of 0.76 (95% CI, 0.73–0.79). The median survival (MoS) was inversely correlated with age, showing a significant decline with advancing age (p < 0.0001). Gender-based survival analysis revealed an MoS of 215 months for males, while it was undefined for females (p < 0.0001). Patients with a single malignancy had an undefined MoS, compared to 105 months for those with two or more malignancies (p < 0.0001). Based on treatment modality, the MoS for patients who received chemotherapy was 66 months, while it remained undefined for those who did not receive chemotherapy (p < 0.0001). Survival analyses based on race, primary site, year of diagnosis, surgery, radiation therapy, and annual household income were not statistically significant. The undefined MoS in certain categories likely reflects insufficient numbers of deaths to calculate the 50% survival probability. Conclusions: Systemic mastocytosis is a rare disease, with only 905 cases identified over 22-years. It shows no gender preference but is more common in older individuals and Caucasians. Improved survival outcomes were observed in younger patients, females, and those with a solitary malignancy, whereas the presence of multiple tumors significantly reduced overall survival (OS). The lower survival rate among patients receiving chemotherapy is likely attributable to its use in more advanced disease stages. Our study highlights the critical need for vigilant monitoring for secondary malignancies in SM patients.