e23299 Background: Brain metastasis in solid malignancies at diagnosis has a poor prognosis. Improvements in the treatment of solid malignancies and advancements in neuroimaging techniques have led to increased incidence of brain metastases. In our study, we examined survival outcomes in patients diagnosed with brain metastasis at the time of diagnosis of primary malignancy at four different sites in the year groups 2010 to 2014 and 2015 to 2020. Methods: Surveillance, Epidemiology, and End Results (SEER) Program 17 registry (November 2022 submission) database was analyzed for four primary sites of cancer based on their high propensity to develop brain metastases- lung and/or bronchus, breast, kidney and/or renal pelvis, and melanoma. Patients diagnosed with malignancy during autopsy or via death certificate and patients with incomplete survival data were excluded. R 4.3.1 software was used for all the analyses. Kaplan-Meier method was used for 2-year survival rate and overall survival analyses. Cox regression analysis was used for hazard ratios (HR). Results: A total of 29,056 and 37,437 cases were identified across the four cancer groups during the period 2010-2014 (Group 1) and 2015-2020 (Group 2), respectively. Lung and/or bronchus tumors comprised the majority of the cases (n = 58,324). 14,811 patients in Group 1 and 18,703 patients in Group 2 received chemotherapy. 8,741 patients in Group 1 and 12,533 patients in Group 2 received radiotherapy. In all the cancers combined, the median survival time in Group 1 was 4 months, and in Group 2 was 5 months. Patients in Group 2 had significantly better survival outcomes than Group 1 (HR:0.81, 95% CI:0.78-0.83, p < 0.001). Table 1 outlines the 2-year survival rates with overall survival p-value. Conclusions: Modest improvement in survival was found in patients diagnosed with synchronous brain metastases during 2015-2020 compared to patients diagnosed in 2010-2014. This slight improvement could be attributed to the improved systemic therapies for cancer, like immunotherapy, as well as advanced local therapy options for brain metastases, although the data for immunotherapy use is unavailable in the SEER database. Overall, the prognosis of synchronous brain metastases remains poor in both groups. Further studies and brain metastases inclusive clinical trials are warranted to improve outcomes in this population. [Table: see text]