Lifetime Occurrence of Brain Metastases Arising from Lung, Breast, and Skin Cancers in the Elderly: A SEER-Medicare Study

Abstract

Background: The Surveillance, Epidemiology, and End Results (SEER) Program recently released data on brain metastases (BM) diagnosed during primary cancer staging workup ("synchronous" BM, or SBM); this study examines the incidence of SBM compared with that of lifetime BM (LBM) identified using Medicare claims for patients diagnosed with lung cancer, breast cancer, or melanoma.

Methods: Incidence proportions (IP) and age-adjusted rates for each of SEER SBM and Medicare LBM are presented along with measures of concordance between the two sources of data, where Medicare LBM were defined by several combinations of diagnosis and putative diagnostic imaging procedure codes.

Results: The SBM IP in lung, breast, and melanoma cancers were 9.6%, 0.3%, and 1.1%, respectively; the corresponding LBM IP were 13.5%, 1.8%, and 3.6%. The greatest SBM IP among patients with lung cancer was 13.4% for non-small cell lung cancer, and among patients with breast cancer was 0.7% for triple-negative breast cancer. The greatest LBM IP among lung cancers was 23.1% in small-cell lung cancer, and among breast cancers was 4.2% for cases of the triple negative subtype.

Conclusions: Using a large dataset that is representative of the elderly population in the United States, these analyses estimate synchronous and lifetime incidence of BM in lung cancers, breast cancers, and melanomas.

Impact: These and other population-based estimates may be used to guide development of BM screening policy and evaluation of real-world data sources.

Figure 1:. Data sources and definitions

Figure 1 shows the years available for each of synchronous and lifetime brain metastasis data sources. Lifetime brain metastasis includes both synchronous brain metastasis diagnosis and cases diagnosed thereafter, whereas synchronous brain metastasis are those diagnosed during staging workup. Data source restrictions led to the use of cases diagnosed in 2010–2012 for estimates of synchronous brain metastasis, but 2008 – 2012 for lifetime estimates.

Figure 2:. Lung and breast cancer incidence proportions of brain metastases by race

This figure illustrates incidence proportions of synchronous brain metastasis as found in SEER data (SEER SBM) and lifetime brain metastases as found in Medicare data (Medicare LBM). In addition to stratification by race, lung cancer incidence proportions are stratified by histology and breast cancers stratified by molecular subtype. “AI” stands for American Indian/Native American; “API”, Asian/Pacific Islander; “WH”, White Hispanic; and “WNH”, White Non-Hispanic. Incidence proportions are not shown where fewer than 11 subjects were available for that proportion. “Her2” stands for Human Epidermal Growth Factor Receptor 2, “Hr” stands for hormone receptors, reflecting either progesterone receptor or estrogen receptor expression status.

Figure 3:. Lung and melanoma incidence proportions by sex

This figure illustrates incidence proportions of synchronous brain metastasis as found in SEER data (SEER SBM) and lifetime brain metastases as found in Medicare data (Medicare LBM). Each of lung cancers and melanomas are presented, stratified by histology and sex. Incidence proportions are not shown where fewer than 11 subjects were available for that proportion. “MMJN” stands for malignant melanoma in junctional nevi; “N & M”, nevi and melanomas.