Purpose: Population-based estimates of the incidence of brain metastases are not generally available. The purpose of this study was to calculate population-based incidence proportions (IPs) of brain metastases from single primary lung, melanoma, breast, renal, or colorectal cancer.
Patients and methods: Patients diagnosed with single primary lung, melanoma, breast, renal, or colorectal cancer (1973 to 2001) in the Metropolitan Detroit Cancer Surveillance System (MDCSS) were used for analysis. IP of brain metastases by primary site and variable of interest (race, sex, age at diagnosis of primary cancer, and Surveillance, Epidemiology, and End Results [SEER] stage of primary cancer) was calculated with 95% CIs.
Results: Total IP percentage (IP%) of brain metastases was 9.6% for all primary sites combined, and highest for lung (19.9%), followed by melanoma (6.9%), renal (6.5%), breast (5.1%), and colorectal (1.8%) cancers. Racial differences were seen with African Americans demonstrating higher IP% of brain metastases compared with other racial groups for most primary sites. IP% was significantly higher for female patients with lung cancer, and significantly higher for male patients with melanoma. The highest IP% of brain metastases occurred at different ages at diagnoses: age 40 to 49 years for primary lung cancer; age 50 to 59 years for primary melanoma, renal, or colorectal cancers; and age 20 to 39 for primary breast cancer. IP% significantly increased as SEER stage of primary cancer advanced for all primary sites.
Conclusion: Total IP% of brain metastases was lower than previously reported, and it varied by primary site, race, sex, age at diagnosis of primary cancer, and SEER stage of primary cancer.