Published in Journal of the National Cancer Institute (2020)
Abstract
Background Squamous cell carcinoma of the anus (SCCA) incidence is rising in the United States. Study of incidence trends by stage at diagnosis, age-specific and birth cohort patterns, and trends in mortality could provide evidence for a true increase and etiological clues for the increase in incidence.
Methods Using the US Cancer Statistics dataset, we examined trends in SCCA incidence (2001–2015) and mortality (2001–2016) rates. Join-point regression was used to compute annual and average annual percentage change (AAPC). Incidence patterns by 5-year age group and birth cohort were evaluated using incidence rate ratios (IRRs) and age-period-cohort modeling.
Results SCCA incidence increased 2.7% per year (95% confidence interval [CI] = 2.1% to 3.3%), with pronounced increases in age groups 50 years and older. Distant-stage SCCA incidence tripled (AAPC = 8.6%, 95% CI = 5.4% to 12.0%, among men and AAPC = 7.5%, 95% CI = 4.8% to 10.2%, among women) and regional-stage SCCA incidence nearly doubled (AAPC = 4.7% for men and women) in both sexes; the AAPC for localized stage was 1.3% (95% CI = 0.6% to 2.0%) in men and 2.3% (95% CI = 1.8% to 2.8%) in women. Compared with adults born circa 1946, recently born black men (born circa 1986) had a nearly fivefold higher risk (IRR = 4.7, 95% CI = 2.1 to 10.2) of SCCA, and the risk doubled among white men (IRR = 2.0, 95% CI = 1.7 to 2.2) and white women (IRR = 2.1, 95% CI = 1.9 to 2.3) born after circa 1960. Anal cancer mortality rates increased 3.1% per year (95% CI = 2.6% to 3.5%) with statistically significant increases in age groups 50 years and older. SCCA incidence-based mortality increased 1.9% annually (95% CI = 0.5% to 3.4%), with a notable (4.9%, 95% CI = 2.4% to 7.3%, per year) rise in adults ages 60–69 years.
Conclusion The increase in SCCA incidence, particularly advanced-stage disease, and a similar increase in mortality suggest a true increase in the occurrence of SCCA. Future research and improved prevention are urgently needed to mitigate the increasing disease burden.