Incidence of intra-axial brain metastases in Eastern Finland

Brain metastases (BM) incidence and characteristics remain poorly defined due to registry data being often incomplete, recording only primary tumors or unspecified metastases. The objective of this study was to examine BM incidence rates and characteristics confirmed by MRI in North Savo, Finland.

In this retrospective study, North Savo residents with first MRI diagnosis of BM between 1 January 2004 and 31 December 2023 were identified through the radiology information system, irrespective of primary cancer diagnosis date. Medical and histopathological records were reviewed. Population person-years were estimated by summing annual end-year counts of all North Savo residents obtained from Statistics Finland. Crude incidence rates and age-standardized incidence rates (ASIRs), standardized to the 2013 European Standard population, were calculated. Temporal trends were assessed using age-adjusted Poisson regression.

Among 516 patients, 474 had histopathological verification. Cancers originating from lung and breast tissue accounted for 56.8% of BM cases. Overall crude incidence was 10.22 (95% CI 9.36-11.15) and ASIR was 9.20 (95% CI 8.42-10.04) per 100,000 person years. ASIR increased from 5.8 in 2004-2008 to 11.8 in 2019-2023. Age-adjusted Poisson regression estimated a 24% increase in incidence per five-year period (incidence rate ratio 1.24; 95% CI 1.14-1.34; P < 0.001). Age-specific incidence peaked at 33.1 per 100,000 person years among patients aged 70-74 years.

MRI-confirmed BM incidence increased over 20 years, despite age standardization. Incidence was highest among older adults. These findings provide contemporary population-based epidemiological data of BM incidence.