Background: Squamous cell carcinoma of the anus (SCCA) incidence is rising in the United States (US). 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 this rise.
Methods: Using the US Cancer Statistics dataset, we examined trends in SCCA incidence (2001-2015) and mortality (2001-2016) rates. Joinpoint regression was used to compute annual and average annual percentage change (AAPC). Incidence patterns by five-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%-3.3%) with pronounced increases in age groups 50 years and older. Distant stage SCCA incidence tripled (AAPC, 8.6% [95% CI = 5.4%-12.0%]) among men and 7.5% [95% CI = 4.8%-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%-2.0%] in men and 2.3% [95% CI = 1.8%-2.8%] in women. Compared to adults born circa 1946, recent born Black men (born circa 1986) had nearly fivefold higher (IRR, 4.7; 95% CI = 2.1-10.2) risk of SCCA and the risk doubled among White men (IRR= 2.0; 95% CI = 1.7-2.2) and White women (IRR, 2.1; 95% CI = 1.9-2.3) born after circa 1960. Anal cancer mortality rates increased 3.1% per year (95% CI = 2.6%-3.5%) with statistically significant increases in age groups 50 years and older. Incidence-based mortality increased 1.9% annually (95% CI = 0.5%-3.4%) with a notable (4.9% [95% CI = 2.4%-7.3%] per year) rise in 60-69-year-old adults.
Conclusion: The rise in SCCA incidence, particularly advanced stage disease, and a similar rise in mortality, suggests a true increase in the occurance of SCCA. Future research and improved prevention is urgently needed to mitigate the rising disease burden.
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