Birth cohort effects in appendiceal adenocarcinoma incidence across the United States.

90 Background: Appendiceal adenocarcinoma incidence rates are increasing across all age groups, sexes and histological subtypes in the United States. Birth cohort patterns of appendiceal adenocarcinomas can provide us with new, etiologic clues into these rising rates but have not been examined for this rare malignant tumor type. We estimated appendiceal adenocarcinoma incidence rates across birth cohorts in the United States. Methods: Using the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program data from eight population-based cancer registries, we identified a total of 4,858 persons aged 20+ years when diagnosed with a pathologically-confirmed primary appendiceal adenocarcinoma (non-mucinous, mucinous, goblet cell, signet ring cell carcinoma) between 1975 and 2019. Birth cohorts (1900-1904 to 1990-1994) were created using five-year age groups and time periods. The ratio of age-specific incidence rates was estimated in each birth cohort relative to the 1945-1949 birth cohort and reported as incidence rate ratios (IRRs) with 95% confidence intervals (CI). Results: Compared to persons born in 1945-1949, appendiceal adenocarcinoma incidence rates more than tripled among persons born in 1980-1984 (IRR 3.41, 95%CI 2.54-4.56) and quadrupled among persons born in 1985-1989 (IRR 4.62, 95%CI 3.12-6.82). For all tumor histological types, age-specific appendiceal adenocarcinoma incidence rates increased across successive birth cohorts after 1945-1949—although to varying degrees reported across histological types (e.g., 1980-1984: mucinous adenocarcinoma: IRR 2.71, 95% CI 1.73-4.26; non-mucinous adenocarcinoma: IRR 2.60, 95% CI 1.46-4.63; goblet cell adenocarcinoma: IRR 4.95, 95% CI 2.77-8.85). Conclusions: There are strong, yet distinct birth cohort effects for appendiceal adenocarcinomas across histological subtypes that remain unexplained. These patterns signal that recent exposure changes may be influencing this increasing disease risk for Generation X and Millennials now entering mid-adulthood. With the trend toward more non-operative management of appendicitis, another significant consideration for providers is to keep occult appendiceal tumors in the differential diagnosis of patients who present in this way. The current absence of appendiceal cancer prevention and screening modalities emphasizes the importance of efforts to support earlier detection in a rare malignancy where clinical trials have been historically very limited. Moreover, as similar trends have been reported in other gastrointestinal cancers, this is also suggestive of potential shared exposures contributing to this rising cancer burden across generations.