The incidence and comparative prognosis of primary cancers with metastasis to non-common sites: A SEER database analysis of 2016-2018

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]