Incidence of brain metastasis at initial presentation of lung cancer

Metastases are the most common tumors of the central nervous system (CNS), with an incidence of approximately 7–14 persons per 100 000 population.1,2 The anatomical specialization of the blood-brain barrier allows the brain and CNS to harbor metastasis less affected by systemic chemotherapy, making it a frequent site for cancer recurrence. It has been reported that 20%–40% of patients with systemic cancer will develop CNS metastasis during the course of their disease.3 Longer survival of cancer patients and advancements in neuro-imaging techniques have contributed to increased detection and ultimately increased incidence of brain metastasis (BM).4 Increases over time have been reported in Sweden.5 Various factors known to affect the epidemiology of BM are primary cancer histology, age at diagnosis, and primary tumor stage.1,6 Higher incidence estimates have been reported for older age groups7 and advancing cancer stage.8 Lung cancer is known to commonly metastasize to the brain, with a range of 10%–36% of all lung cancers developing BM during the course of their disease.2,9–11 However, the incidence is thought to be underestimated due to numerous factors including difficulty of tracking and recording the life-time incidence and incomplete reporting in cancer databases. Although there are investigations from clinical trials and single institutions providing incidence and frequency of BM, there have been limited population-based data.8,12 The average survival of patients with BM is low (<6 months), which makes it crucial to identify this patient population for effective surveillance, preventive measures, and resource allocation.1,6 Knowing the frequency of BM during the spectrum of care can potentially inform treatment, insight into cancer metastasis, and health care policy. Recent changes in population-based data collection initiated by cancer surveillance agencies in the United States (American College of Surgeons' Commission on Cancer, NCI's Surveillance Epidemiology and End Results [SEER] Program, and Centers for Disease Control and Prevention's National Program of Cancer Registries) have required data collection for secondary metastatic sites including brain. We sought to identify metastases using 2 different registries from 2 countries to report the first population-based study on the initial presentation of lung cancer. We report sites of selected disease involvement with a focus on BM.