Chapter 4: Cancer incidence in Canada: trends and projections (1983-2032) – Cervix cancer - HPCDP: Volume 35, Supplement 1, Spring 2015

Chapter 4: Projections by Cancer Site

11. Cervix cancer

Cervix cancer was responsible for 0.9% of all new Canadian cases of cancer and 1.8% of cancer cases in females, with an average of 1345 new cases annually in 2003–2007 (Table 4.11.1). One in 145 females can expect to develop the disease in her lifetime, and 1 in 443 females are likely to die from it.^{Endnote 1} During 1998–2007, the ASIRs for cervix cancer decreased significantly by 1.4% per year (Figure 3.2). The 5-year relative survival rate for cervix cancer was 74% in Canada between 2006 and 2008.^{Endnote 1}

The pattern of age-specific rates of cervix cancer differs from those of most others cancers. Women aged 45 or older experienced almost double the incidence rate of their younger counterparts in 2003–2007 (Table 4.11.2).

However, the number of cases decreased significantly with age (Table 4.11.1). The observed incidence rates decreased in all age groups, at approximately similar levels for age groups 45 and over (Figure 4.11.2). The predictions indicate that the incidence rates will decrease with time and then level off in each age group. The rates are projected to decrease with age in each period for women aged 45 and over (Figure 4.11.2). Women aged 85 or older will eventually experience rates as low as those in the youngest age group.

In all regions, the incidence rates have decreased with time, at similar degrees (Figure 4.11.1). The projections show that British Columbia will continue to have the lowest rates, while the Prairies will experience the highest incidence after 2008–2012.

From 2003–2007 to 2028–2032, the ASIRs of cervix cancer for Canada are expected to decrease by 20%, from 7.6 to 6.1 per 100 000 (Table 4.11.2). With the projected Canada population growth and aging, however, the annual number of new cases is predicted to increase by 7%, from 1345 to 1435 (Table 4.11.1).

Comments

The 2013 IARC summary concludes that there is sufficient evidence for the human carcinogenicity of HPV types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58 and 59 in the cervix.^{Endnote 47} Virtually all cervical cancers are causally linked to HPV.^{Endnote 166} HPV types 16 and 18 cause approximately 70% of all cervical cancers.^{Endnote 167, Endnote 168} The overall HPV prevalence was estimated at 16.8% in females in British Columbia, with the prevalence of high-risk HPV at 13.9%.^{Endnote 169} HPV DNA point prevalence is thought to underestimate cumulative incidence of infection as many infections resolve spontaneously. People with immunosuppression caused by human immunodeficiency virus (HIV) infection or organ transplantation are also at increased risk.^{Endnote 170} Cigarette smoking generally doubles the risk of developing the disease, with dose response trends for both smoking frequency and duration.^{Endnote 52} About 7% of cervical cancer cases were attributed to smoking in the UK in 2010.^{Endnote 171}

Cervical cancer incidence rate has dropped significantly due to general population screening with the Papanicolaou (Pap) test that allows early detection and treatment of precancerous lesions. The 2013 Annual Report to the Nation on the Status of Cancer^{Endnote 56} shows that the prevalence of the Pap test is negatively associated with cervical cancer incidence rates in the US but positively associated with vaccination coverage levels. Information on cervical cancer screening has not been included in the statistical projections in this report, but cervical cancer screening has been widespread in Canada for many decades and therefore its impact on future trends of cervical cancer incidence has been taken into account to some extent through observed incidence rates. Cervical cancer rates should fall even faster, as the effects of HPV vaccinations come into play. A recently introduced vaccine has been shown to reduce the risk of infection with HPV types 16 and 18. The reduction in incidence rates that might be expected for newly vaccinated cohorts depends on the eligibility and coverage as well as the percentage of cancers prevented by the vaccine.^{Endnote 172} The primary age group recommended for HPV vaccination is females aged 9 to 13. The vaccination is also recommended for females aged 14 to 26 as there still is the potential for benefit regardless of previous history of sexual activity.^{Endnote 173} Women aged 20 to 24 would be included in the lower risk cohorts by 2020 and those aged 30 to 34, by 2030. If the vaccine prevents 70% of new cervical cancers^{Endnote 173} and population coverage is 60%,^{Endnote 60} the reduction in the incidence rate for all ages combined will be minimal by 2020, but the incidence rate is estimated to be reduced by about an additional 7% by 2030, from 6.1 to 5.5 per 100 000.