Highlights
- Prevalence is a complex measure that depends on incidence and survival.
- Because they are 2 of the 4 most common cancers diagnosed and have good survival, 10-year prevalence for prostate and female breast cancers is high in Ontario.
- It is important to plan to meet the ongoing needs of people who are living with and beyond cancer.
Cancer prevalence is a complex measure of disease burden that is often misunderstood, yet important to consider when planning cancer policies and resources. At its most basic level, it describes the number of people in a population who have been diagnosed with cancer in a given time period and who are still alive on a given date.
Individuals included in a prevalence count are extremely diverse. Estimates of prevalence for a 10-year period represent a mixture of individuals at different stages of the cancer experience, from those newly diagnosed through to long-term survivors. The many factors that influence prevalence — including, incidence (new diagnoses), survival, population growth and aging, and changes in cancer treatment and detection — also contribute to its complexity.
Interpreting prevalence over time can be challenging because these factors can change independently. For example, improvements in cancer treatment or an increase in number of cancers diagnosed could result in an increase in prevalence, and a decrease in cancer risk could result in a decrease in prevalence. Changes in incidence will have a major impact on short duration (2 or 5-year) prevalence, while improvements in survival will be more pronounced in longer duration (10-year) prevalence. Generally speaking, prevalence counts tend to be highest for the most common cancers with the longest survival, and less common cancers with longer survival may have higher prevalence counts than common cancers with shorter survival.
Prostate and female breast cancers are the 2 most prevalent cancers in Ontario because they are among the 4 most common cancers diagnosed and have good survival — in Ontario, approximately 74,800 men and 66,500 women had been diagnosed with prostate and breast cancer, respectively, between January 1, 2002 and December 31, 2011, and were still alive as of January 1, 2012.
The rest of the 10 most prevalent cancers in Ontario are colon and rectum, thyroid, melanoma, lung, non-Hodgkin lymphoma, body of uterus, bladder and kidney.
Colorectal cancer is among the top 4 most common cancers diagnosed in Ontario, but due to its lower survival, it has a lower prevalence than prostate and female breast cancers. Ten-year prevalence for colorectal cancer was about 42,700 as of January 1, 2012.
Lung cancer is also among the top 4 most common cancers diagnosed in Ontario, with approximately 9,460 new cases in 2011, but it has very poor survival. The prevalence count for lung cancer is lower than for cancers of thyroid and melanoma of the skin, which are less commonly diagnosed (3,230 and 3,170 new cases in 2011, respectively) and have high survival. Kidney cancer is the only cancer that is included in the top 10 cancers for prevalence and not the top 10 cancers for incidence; leukemia has greater incidence but has lower survival.
On January 1, 2012, there were over 350,000 people living in Ontario who had been diagnosed with cancer in the previous 10 years. It is clear that adequate planning is essential to ensure that resources and services meet the ongoing needs of the growing number of people living with and beyond cancer. Their healthcare needs vary and include active treatment, follow-up and treatment of recurrences, and end-of-life or palliative care. Prevalence is 1 of many indicators of the burden of cancer for individuals, families and health services.