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Primary tumors have common sites of metastasis such as lymph nodes, bones, liver, lungs, and brain; however, they can also metastasize to other uncommon sites such as adrenals, bone marrow, and skin among others. Our study aimed to investigate the relationship between uncommon sites of metastasis at the time of diagnosis and median survival in a number of primary tumors using the Surveillance, Epidemiology, and End Results (SEER) database. This retrospective cohort study conducted between September-October 2021 included patient-level SEER data for 2016-2018 using SEER Research Data, 9 Registries, Nov 2020 Sub (1975-2018). Descriptive analysis for complete cohort and median survival for each primary within the cohort was performed using R software. A total of 25,345 patients (females, 51.4%) were diagnosed with primary tumors with metastasis to uncommon sites at the time of diagnosis; the mean age at diagnosis was 68 years. Lung and bronchus primaries constituted the largest proportion of cohort (41.9%) that metastasized to uncommon sites, followed by nonHodgkin lymphoma-nodal (7.4%), pancreas (6.6%), stomach (3.7%), and ovarian (3.4%). The incidence of metastasis to uncommon sites was most common in respiratory cancers in ages 61-80 years (25%) and least in breast primaries in ages 18-40 years (0.1%), and was higher in Whites compared to other races. Regarding median survival, liver cancer with metastasis to uncommon sites had the worst prognosis (1 month), whereas small intestine tumors were associated with a better prognosis, median survival of 13 months. In this cohort study, the lung and bronchus cancers were the most common primaries metastasized to uncommon sites at diagnosis. The liver tumor had the worst survival compared to other tumors. These findings will help redirect the available screening tools to improve survival in patients with primary tumors with metastasis at diagnosis and may also play an essential role in future research and achieve a better prognosis for cancer patients.

e22506 Background: Primary tumors can present late with metastasis to uncommon sites (such as adrenals, bone marrow, pleura, malignant pleural effusion, peritoneum, and skin, among others) as well as common sites (such as liver, bone, lung, and distal lymph nodes). Our study aimed to investigate the characteristics and comparative survival for metastasis to uncommon sites at the time of diagnosis using the Surveillance, Epidemiology, and End Results (SEER) database. Methods: We extracted the data from the SEER database for the years 2016-2018 to include all patients presenting with metastasis to uncommon sites at diagnosis without restrictions on age, race, year of diagnosis, or histological type. Uncommon sites of metastasis were coded as other sites in the SEER database and did not involve liver, bone, brain, lung, and distal lymph nodes. We used R software to perform the descriptive analysis for uncommon sites according to the primary sites and co-metastasis along with their survival. Results: A total of 25,345 patients were included with metastasis to uncommon sites with a female predominance of 13,033 (51.4 %); the mean age at diagnosis was 68 ± 17 years. Lung and bronchus primaries represented the largest proportion with metastasized to uncommon sites 10,612 (41.9%), followed by non-Hodgkin's lymphoma-nodal 1,871 (7.4%), pancreas 1,690 (6.6%), stomach 940 (3.7%), and ovarian 885 (3.4%). The incidence was most common in respiratory cancers in ages 61-80 years (25%) and least in breast primaries in ages 18-40 years (0.1%). Whites compared to other races had a higher incidence. Liver cancer had the worst prognosis with a median survival of 1 month, whereas small intestine tumors were associated with a better prognosis with a median survival of 13 months. Further survival data is mentioned in the table. Conclusions: Our study concluded that the lung and bronchus cancers were the most common primaries metastasized to uncommon sites at diagnosis while the liver had the worst survival. These findings will help redirect the available screening tools to improve survival in patients with primary tumors with metastasis at diagnosis and may also play an essential role in future research and achieve a better prognosis for cancer patients.[Table: see text]