Abstract
BACKGROUND: Breast cancer is the most prevalent cancer in women worldwide. Despite it having an etiology that has fixed, genetic as well as modifiable, environmental risk factors, the narrative around breast cancer prevention emphasizes gendered interpretations of the etiology, such as "reproductive factors cause breast cancer" and women should change their behaviors to reduce their risk. Since migrant studies can distinguish environmental from genetic risk factors, we conducted a structured review of migrant studies and assessed prominent cancer website resources to determine evidence of gender bias between breast and prostate cancer. METHODS: We searched ten online databases for articles with migration as the exposure and breast cancer mortality and/or incidence as the outcome. We also searched using prostate cancer as the outcome to generate a comparison group. We developed rubrics to categorize the studies by study design (single, double, and time dimensional), convergence (a change in incidence or mortality for the migrant population), and concordance (consistency between results and author-attributed etiology). We used chi-square tests to test for differences by cancer type. We web-scraped four notable cancer websites to extract website layouts, risk factor information, and language describing breast cancer etiology and compared it to the content used for prostate cancer. FINDINGS: Of all 140 studies and 220 comparisons, breast (n = 131) outnumbered prostate cancer studies (n = 89; p-value = 0·005). For both cancers, studies that compared all three populations (the non-migrant, origin, and destination population outcomes) or measured length of stay demonstrated that cancer rates converged with migration. Most authors attributed breast cancer etiology to genetic and environmental factors. Yet, the migrant study results were inconsistent with public health messaging; all four websites framed breast cancer as more modifiable than prostate cancer. CONCLUSION: Research efforts and public health messaging for breast cancer should consider gendered barriers to changing individual-level risk factors and develop more prevention strategies at the health systems level.