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

Chapter 4: Projections by Cancer Site

4. Colorectal cancer

Colorectal cancer is the third most common cancer for both males and females in Canada. In 2003–2007, the average annual number of new cases of colorectal cancer in Canada was 10 620 in males and 9010 in females, 13.1% and 12.1% of all male and female cases, respectively (Tables 4.4.1 and 4.4.2, Figure 3.9). Slightly more than two thirds of new cases of colorectal cancer were cancers of the colon. One in 13 males and 1 in 15 females can expect to be diagnosed with colorectal cancer in their lifetime, and 1 in 29 males and 1 in 31 females can expect to die from it.^{Endnote 1} The 5-year relative survival rate following a diagnosis of colorectal cancer was 65% in 2006–2008.^{Endnote 1}

In both males and females, the overall incidence rates of colorectal cancer have continued to decrease since 1983–1987, although the decrease was interrupted between 1993–1997 and 1998–2002 (Figure 4.4.1). This pattern appeared for all regions except in Atlantic Canada, where male rates in the last 2 observed periods increased slightly. From 2000 to 2007, colorectal cancer rates in Canada decreased significantly in both males and females by 0.8% per year (Figures 3.1 and 3.2).

Like most other cancers, the occurrence of colorectal cancer is strongly related to age, with 87% of cases in people 55 or older in 2003–2007. The ASIRs rose steeply with age, from 3.1 per 100 000 in males aged under 45 to 510.3 per 100 000 for those aged 85 and over and, correspondingly, from 2.9 to 394.9 per 100 000 in females (Tables 4.4.3 and 4.4.4).

The incidence rates in males and females were almost the same in those under 45 (Figure 4.4.2). Above this age, the male-to-female incidence rate ratio increased with age to 1.6:1 in the 65–74 age group and then decreased to 1.3:1 in those aged 85 or older.

The predictions indicate that the incidence rates of colorectal cancer for both males and females will marginally decrease and then stabilize in most regions of Canada except Quebec, where rates will show a relatively striking decrease (Figure 4.4.1). Only male rates in the Atlantic region are predicted to increase until 2013–2017, followed by a levelling off. Internal ranking of the ASIRs in geographical areas is projected to be similar for both sexes, with elevated rates in the Atlantic region, where the highest rates will be in Newfoundland and Labrador, and the lowest rates in British Columbia. The long-term trends of the rates are projected to approach convergence everywhere except in the Atlantic region.

The rates are expected to rise in younger people (<55), displaying a downward trend in the under 45 age group after 2018–2022 in males and 5 years later in females. The rates will decrease in the opposite ages (≥55), showing a reverse trend in 55–64 age range after 2018–2022 in men and 5 years sooner in women.

From 2003–2007 to 2028–2032, the ASIRs of colorectal cancer for Canada are expected to decrease by 6% in both sexes, from60.8 to 57.0 per 100 000 for males and from 41.0 to 38.6 per 100 000 for females (Tables 4.4.3 and 4.4.4). Because of projected Canada population growth and aging, the annual number of new male cases is predicted to increase by 87%, from 10 620 to 19 815, and the number of new female cases, by 69%, from 9010 to 15 260 (Tables 4.4.1 and 4.4.2).

Comments

The decrease in colorectal cancer incidence likely reflects changes in prevalence of risk and protective factors and screening uptake. Lifestyle factors play a major role in colorectal cancer etiology. These risk factors include high consumption of red and processed meat, alcohol, smoking, obesity and physical inactivity.^{Endnote 47, Endnote 84, Endnote 85} High intake of fruit and vegetables may be protective.^{Endnote 86, Endnote 87} Since the early 1960s, annual per capita red meat consumption rates in Canada increased by 25% from 65 kg (carcass weight) in 1963 to 81 kg in 1976, but has since dropped by 30% to 56 kg in 2009.^{Endnote 81} The proportion of Canadians who were at least moderately active increased from 39% in 1994/1995 to 52% in 2003, then stabilized in 2005.^{Endnote 88} A decrease in smoking prevalence began in the mid-1960s in males and in the mid-1980s in females in Canada.^{Endnote 42, Endnote 43} These risk factor changes may partly account for the decrease in incidence.

The use of hormone replacement therapy (estrogen plus progesterone) by women appears to reduce colorectal cancer risk;^{Endnote 89} this may partially explain the lower incidence in females than in males, especially in those older than^{Endnote 55}. In addition, compared with males, females in Canada have been engaging in healthier eating patterns.^{Endnote 90 Endnote 91} This may also contribute to the gender difference in colorectal cancer risk. Known modifiable risk factors and genetic factors explain only a fraction of colorectal cancer cases.^{Endnote 36}

The decrease in colorectal cancer incidence rates may also result from the introduction or increased use of screening that allows the detection and removal of adenomatous polyps.^{Endnote 92, Endnote 93} The screening rates increased from 2005 to 2008 in most provinces in Canada.^{Endnote 94} In 2008, 32% (range: 16%–46%) of Canadians aged 50 to 74 reported having either a fecal occult blood test (FOBT) in the past 2 years or a sigmoidoscopy/colonoscopy in the past 5 years.^{Endnote 36, Endnote 94} Uptake of screening in Canada lags behind that in the US.^{Endnote 36, Endnote 95} As of 2010, all provinces had announced or started implementing organized colorectal cancer screening programs. It should be noted that these estimates may change with the increased use of screening in the near future, which may result in more colorectal cancer cases being diagnosed in the early stages.