Recent Trends in Squamous Cell Carcinoma of the Anus Incidence and Mortality in the United States, 2001-2015

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.

Figure 1.

Age- and race-specific incidence rates* of squamous cell carcinoma of the anus (SCCA): National Program of Cancer Registries and Surveillance, Epidemiology, and End Results Program (2001–2015). Age-specific SCCA incidence rates according to diagnosis during the calendar periods 2001–2005, 2006–2010, and 2011–2015. A–F) incidence rates among non-Hispanic white men, non-Hispanic white women, non-Hispanic black men, non-Hispanic black women, Hispanic men, and Hispanic women, respectively. *Rates were calculated as number of cases per 100 000 person-years and age adjusted to the 2000 US standard population. †Data suppressed because there were fewer than 16 cases in the time interval.

Figure 2.

Trends in the annual incidence rates* of squamous cell carcinoma of the anus (SCCA) according to age and stage at diagnosis among men and women: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results Program (2001–2015). Data markers represent the observed incidence rates (cases per 100 000 person-years) of SCCA. A and B) SCCA incidence trends according to age at diagnosis in men and women, respectively. C and D) SCCA incidence trends according to the stage at diagnosis in men and women, respectively. *Rates are age-adjusted to the 2000 US standard population. †Indicates statistically significant incidence trend (P < .05).

Figure 3.

Stage distribution of squamous cell carcinoma of the anus (SCCA) among men and women: National Program of Cancer Registries and Surveillance, Epidemiology, and End Results Program (SEER) (2001–2015). Vertical bars represent proportion of SCCA cases diagnosed by SEER summary stage (localized, regional, distant, and unknown) among men (A) and women (B).

Figure 4.

Incidence rate ratios (IRRs) by birth cohort for squamous cell carcinoma of the anus (SCCA; referent cohort = 1946): National Program of Cancer Registries and Surveillance, Epidemiology, and End Results Program (2001–2015). Shaded bands indicate 95% confidence interval. A–F) IRRs among non-Hispanic white men, non-Hispanic white women, non-Hispanic black men, non-Hispanic black women, Hispanic men, and Hispanic women, respectively. *Not reported because there were fewer than 16 cases in the time interval.