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

Chapter 4: Projections by Cancer Site

1. Oral cancer

Oral cancers are also referred to as cancers of the buccal cavity and pharynx. In 2003–2007, the average annual number of new oral cancer cases was 2285 in males and 1085 in females (Tables 4.1.1 and 4.1.2), accounting for 2.8% and 1.5% of all male and female cancer cases, respectively.

Oral cancer was the ninth most common cancer for males and the fourteenth most common in females in that period. The lifetime risk of developing oral cancer is about 1 in 67 for males and 1 in 137 for females.^{Endnote 1} Within oral cancers the percentages of cases in 2007 by subsite were lip (9%), tongue (25%), salivary gland (11%), mouth (19%), nasopharynx (7%), oropharynx (4%), and other and unspecified (23%).^{Endnote 1} The male-to-female ratio of ASIRs in Canada has decreased rapidly, from 3.3:1 in 1983–1987 to 2.4:1 in 2003–2007 for all ages combined (Figure 4.1.1).

In 2003–2007, the incidence rates of oral cancer were low for both males and females aged under 45 (Tables 4.1.3 and 4.1.4).

Rates increased steeply up to ages 70 to 74 and then rose slowly. The majority of cases (72% in men and 73% in women) occurred in people aged 55 or over (Tables 4.1.1 and 4.1.2). The 5-year relative survival rates for oral cancer diagnosed between 2006 and 2008 were 61% formales and 68% for females.^{Endnote 1}

In males, incidence rates of oral cancers have decreased over the observation period, falling from 18.8 per 100 000 in 1983–1987 to 12.6 in 2003–2007 (Figure 4.1.1). The decreased trends accelerated with age in males (Figure 4.1.2). Across the country, the largest decrease was observed in the Prairies. Rates of oral cancers have decreased marginally in females.

From 1998 to 2007, the ASIRs for oral cancers have significantly decreased by 1.0% per year in males and have remained relatively static in females (Figures 3.1 and 3.2). The trend pattern by sex is similar for all age groups except in the group younger than 45 (Figure 4.1.2).

The ASIRs for oral cancer in Canadian males are projected to continue to fall in all age groups above 45, but beginning to increase after 15 years for the group aged between 45 and 54 (Figure 4.1.2). However, the projections in the young age groups may be affected by random error from the small number of cases in these age ranges. The rates in females will remain stable in each age group (Figure 4.1.2). Oral cancer rateswill continue to be significantly higher for males than for females, but the male-to-female ratio will decrease to 2.2:1 in 2028–2032.

Figure 4.1.1 illustrates the inter-regional variation of ASIRs for oral cancer. The predictions indicate that the rates of oral cancer in males will continue to gradually decrease and then stabilize in all regions. The rates in the Prairies will have dropped from being the highest in the country in 1983–1987 to the lowest as of 2008–2012. In females, the rates are projected to decrease in British Columbia and, to a lesser extent, in the Prairies, but are likely to increase in the Atlantic region and Quebec, and remain stable in Ontario. The ASIRs for females will be 4.4 per 100 000 in British Columbia and 4.9–5.8 per 100 000 in the other regions by 2028–2032. In general, the incidence rates are projected to be higher in eastern Canada than in western Canada.

From 2003–2007 to 2028–2032, ASIRs for Canada are predicted to decrease by 6% in males, from 12.6 to 11.8 per 100 000, and to remain stable in females, changing only from 5.2 to 5.3 per 100 000 (Tables 4.1.3 and 4.1.4). Due to the projected Canada population growth and aging, the annual number of cases is estimated to increase by 57% in males, from 2285 to 3595, and by 62% in females, from 1085 to 1760 (Tables 4.1.1 and 4.1.2).

Comments

The major risk factors for oral cancer (except salivary gland, nasopharyngeal and lip cancers) are tobacco and alcohol use.^{Endnote 47, Endnote 48, Endnote 49, Endnote 50} In 2011, the age-standardized prevalence of current smoking in Canadians aged 12 or older was 23.0% for males and 17.9% for females, with crude rates of 22.3% and 17.5%, respectively.^{Endnote 51} A decrease in smoking prevalence began in the mid-1960s in males and in the mid-1980s in females.^{Endnote 42, Endnote 43} The decrease in smoking likely accounts for the downward trends in male oral cancer incidence. For females, the impact of decrease in smoking is largely not yet reflected in the incidence data used for the projections, given the lag of at least 20 years between the fall in smoking rates and the decrease in oral cancer incidence rates. It is likely that incidence rates in females will begin to drop as well over the longer term.

Human papilloma virus (HPV), particularly HPV type 16, is a risk factor for oropharyngeal cancer, and Epstein-Barr virus (EBV) is a risk factor for nasopharyngeal cancer. ^{Endnote 52, Endnote 53} Oropharynx cancer is increasing in incidence in Canada,^{Endnote 54, Endnote 55} with a decreasing age at diagnosis.^{Endnote 55} This increase has also been reported in the United States (US),^{Endnote 56} Denmark^{Endnote 57} and Korea,^{Endnote 58} where HPV-unrelated oral cancers have decreased. A change in sexual behaviour that increases oral exposure to HPV may be one reason for the rise in HPV-associated oral cancers.^{Endnote 54} Since the fall of 2008, all provinces and territories have introduced HPV immunization programs for girls into their routine immunization schedules (see more in Section 11).^{Endnote 59} The vaccination coverage has increased significantly in Ontario since the program was initiated in the 2007.^{Endnote 60} HPV vaccination and the upward trend in coverage may cause a decrease in rates of HPV-associated oral cancers in the future. The contributions of other risk factors for oral cancers, including diet and sun exposure (linked to lip cancer), are unclear.