Cancer in Ontario

Key findings

The number of people living with cancer in Ontario continues to increase. Evidence shows that the ten-year cancer prevalence for four most common cancers have increased slightly and the 5-year relative survival for 14 common cancers has improved over time. Screening and preventive measures continue to play an important role in cancer control.

How do incidence, mortality, survival and prevalence relate to one another?

• Incidence is a measure of cancer risk in the population.
• Mortality is determined by both incidence and prognosis .
• Cancer survival in a population is usually expressed as five-year relative survival.
• Prevalence is determined by both incidence and survival.

See Technical Information for more details on our analysis.

Incidence

• The annual number of new cancer cases diagnosed in Ontario has more than doubled since 1983, with 74,044 new cancer cases estimated to be diagnosed in 2013. The majority of this increase is due to population growth and population aging (cancer risk increases with age), with a much smaller proportion attributed to increases in cancer incidence rates (Figure 1).
• Cancer risk in a population is related to many things in addition to age:
  • Prevalence of important modifiable risk factors, such as tobacco use or obesity
  • Uptake of human papilloma virus (HPV) vaccines
  • Screening patterns
  • Social and physical characteristics, such as sexual behaviours, age at menopause and number of children
  • Exposures to carcinogens such as asbestos in the workplace or environment
  • Genetics
• Changes in some of these underlying factors over time result in changes to incidence rates
  • Making direct connections between exposure to risk factors and cancer can be difficult, however, because cancer can develop quickly or slowly after exposure.
    • Lung cancer rates, for example, typically take many years to reflect changes in provincial smoking rates.
  • Rapid uptake of screening can result in an apparent sudden rise in cancer diagnoses, as cancers are discovered earlier than they otherwise would have been.
• In 2009, the most commonly diagnosed cancers in Ontario for males were prostate (28%), colon and rectum (13%) and lung (13%). For females, the most common cancers were breast (26%), lung (12%), and colon and rectum (11%). (Figure 2)

Mortality & Survival

• In 2009, chronic diseases—including cancers, cardiovascular diseases, chronic respiratory disease and diabetes—were responsible for 78% of all deaths in Ontario. Of these, cancer accounted for the largest proportion (39%), closely followed by cardiovascular disease (38%) (Figure 3).
• Mortality rates may reflect both trends in underlying risk factors, and population-level or individual-level interventions such as screening and treatment.
• Two cancers may have similar survival ratios but different mortality rates. For example, lung and esophageal cancer have similar survival, but lung cancer has a much higher mortality because of the high number of cases diagnosed.
• In addition, two cancers may have similar incidence but different survival. For example, lung and colorectal cancers occur with approximately equal frequency, but lung cancer is much more common as a cause of death because of its poorer survival.

Relative Survival

• Relative survival is a ratio, comparing the survival experience of individuals with cancer to that of the general population of the same age and sex; it shows the extent to which cancer shortens life; it is often age-adjusted to account for the fact that the risk of death increases as we age, and that the population has aged over two compared time periods.
• As a result of advances in detection (including organized screening) and treatment, the relative survival ratio for most common cancers has improved in Ontario (Figure 4).
• The two exceptions are survival for cancers of the uterus and urinary bladder, for both of which survival has remained essentially stable:
  • Other jurisdictions have noted stable or decreasing trends in comparable timeframes e.g. USA ^1,2, Europe ³ and South Australia ⁴.
  • There is survival variation between the two main types of bladder cancer: papillary transitional cell carcinoma (PTCC) and non-papillary transitional cell carcinoma (NPTCC). PTCC has a higher survival ratio than NPTCC. There is evidence that the proportion of papillary cases has decreased while the proportion of non-papillary has increased over time.
• In spite of improvements, relative survival for certain cancers still remains low. Most notable is relative survival for cancers of the pancreas, lung and bronchus, and stomach, for which relative survival remains less than 30%.
• It is important to note, however, that survival for prostate, thyroid, melanoma of the skin, and female breast cancers is quite high—at 87% or higher relative survival five years after diagnosis. Prostate and thyroid cancer 5-year survival ratios are both over 97%.

Conditional 5-year Relative Survival

• Conditional 5-year relative survival describes the probability of surviving an additional 5 years at various points in the cancer experience, after adjusting for the expected survival for people of the same age, sex, and time period in the general population.
• For those patients who have already survived several years after diagnosis, conditional survival estimates generally provide more realistic survival expectations than the more typical relative survival statistics. This is because these patients have already lived past the time when the risk of dying was greatest – soon after diagnosis.
• Figures 5, 6, and 7 show the conditional 5-year relative survival graphs for male colorectal, female colorectal and female breast cancer, respectively. These estimates are graphed together with the relative survival ratios to illustrate how each changed over time.
• At the time of diagnosis, males and females with colorectal cancer have a 65.2% and a 66.4% chance, respectively of surviving 5 years compared with the general population (Figure 5, 6). In contrast to the relative survival curve that decreases continuously over time, most steeply in the first few months and then the first 3 years post-diagnosis, the conditional 5-year relative survival curves show that males and females experience notable improvements in relative survival as the time since diagnosis increases. For example, a male patient who has survived 2 years after diagnosis of colorectal cancer now has a roughly 81% chance of surviving 5 more years. After 5 years, males previously diagnosed with colorectal cancer have nearly the same chance of surviving 5 more years as the general population (~ 95%).
• Figure 7 shows that, in contrast to colorectal cancer, female breast cancer shows a very good 5-year relative survival (87%) at the time of diagnosis but after 5 years, females previously diagnosed with breast cancer have a 94% chance of surviving an additional 5 years compared to the general population.

Prevalence

• Prevalence is the number of patients alive at any given time who have been diagnosed with cancer during a specific earlier time frame.
• Both incidence and survival influence prevalence.
• A measure of the population burden of cancer, prevalence includes people in various phases:
  • active treatment
  • post-treatment in regular follow-up
  • long-term survivors no longer in active cancer follow-up
  • those being treated for recurrences
  • those near the end-of-life
• Prevalence is high for prostate and breast cancers (Figure 8). As of January 1, 2010, there were approximately 71,500 men living in Ontario who had been diagnosed with prostate cancer and 63,000 women living in Ontario who had been diagnosed with breast cancer within the last 10 years. The prevalence estimates for both of these cancers are high because they are common cancers and because they both have very good survival.
• Although colorectal cancer is one of the most common cancers in Ontario, prevalence for this cancer, with about 40,000 cases diagnosed within the last 10 years in people still living in Ontario as of January 1, 2010, is substantially lower than for prostate and breast cancer. The lower prevalence of colorectal cancer reflects lower survival ratios for this cancer.
• Of the most common cancers in Ontario, lung cancer has the lowest prevalence, reflecting poor lung cancer survival.
• In spite of increasing cancer incidence, more Ontarians are surviving cancer with every passing year because of more effective treatments and early detection. As a result, many cancers are now being managed as chronic conditions. This hopeful news brings with it new challenges in terms of resources and services to meet the ongoing needs of people living with and beyond cancer.

View Notes

1. Howlader N, Noone AM, Krapcho M, Neyman N, Aminou R, Altekruse SF, Kosary CL, Ruhl J, Tatalovich Z, Cho H, Mariotto A, Eisner MP, Lewis DR, Chen HS, Feuer EJ, Cronin KA (eds). SEER Cancer Statistics Review, 1975-2009 (Vintage 2009 Populations), National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/csr/1975_2009_pops09/, based on November 2011 SEER data submission, posted to the SEER web site, April 2012, updated August 20, 2012. [cited 2013 February 19]
2. David K, Mallin K, Milowsky M, Ritchey J, Carroll P, Nanus D. Surveillance of urothelial carcinoma: stage and grade migration, 1993–2005 and survival trends, 1993–2000. Cancer. 2009 Apr 1: 115(7):1435–47.
3. Karim-Kos H, de Vries E, Soerjomataram I, Lemmens V, Siesling S, Coebergh J. Recent trends of cancer in Europe: a combined approach of incidence, survival and mortality for 17 cancer sites since the 1990s. European Journal of Cancer. 2008 Jul; 44(10):1345–89.
4. Luke C, Tracey E, Stapleton A, Roder D. Exploring contrary trends in bladder cancer incidence, mortality and survival: implications for research and cancer control. Journal of Internal Medicine. 2010 May; 40(5): 357–62.