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

Chapter 4: Projections by Cancer Site

13. Ovarian cancer

Ovarian cancer was the seventh most common cancer in Canadian females and the second most frequently diagnosed gynecological malignancy in 2003–2007. One in 68 females can expect to be diagnosed with ovarian cancer in their lifetime, and 1 in 95 females are estimated to die from it.^{Endnote 1} The average annual number of new ovarian cancer cases in this period was 2385, equivalent to 3.2% of all cancer cases in females (Table 4.13.1).

In 2003–2007, incidence of ovarian cancer increased sharply with advancing age to a plateau in those aged 75 or older (Table 4.13.2).

About 70% of the new cases were diagnosed in women aged 55 or older (Table 4.13.1). Ovarian cancer is the most lethal gynecological cancer. The 5-year relative survival rate was 45% in 2006–2008.^{Endnote 1}

Incidence rates of ovarian cancer in Canada have decreased very slightly since 1983–1987 (Figure 4.13.1).

During 1998–2007 ASIRs for ovarian cancer were relative stable, declining non-significantly by 0.2% per year (Figure 3.2). The trends in age specific ASIRs shown in Figure 4.13.2 illustrate relatively stable rates over time. Regional comparison of incidence does not reveal any geographical patterns before 1998–2002 but does show that rates diverge during 2003–2007 (Figure 4.13.1). Elevated incidence rates of ovary cancer were seen in Ontario, whereas the lowest rates appeared in the Atlantic region.

The overall Canadian incidence rates of ovarian cancer are projected to stabilize in the next 25 years (Figure 4.13.1). While Quebec will experience a substantial fall in rates, the rates in other regions will be stable or decrease marginally. The age specific incidence rates show that the predicted reduction of ASIRs in each age group is less pronounced (Figure 4.13.2).

From 2003–2007 to 2028–2032, the ASIRs for ovarian cancer for Canada are expected to decrease by 4%, from 11.6 to 11.1 per 100 000 (Table 4.13.2), but the annual number of cases is projected to increase by 53%, from 2385 to 3650 (Table 4.13.1) as the Canadian population grows and ages.

Comments

The etiology of ovarian cancer is poorly understood;Endnote 183 however, numerous risk factors are associated with either an increased or decreased likelihood of developing the disease. The known risk factors for the disease include reproductive and genetic components.Endnote 184, Endnote 185 Uninterrupted and prolonged ovulary cycles increase ovarian cancer risk.Endnote 186, Endnote 187 Long-term (≥5 years) use of hormone replacement therapy increases the risk.Endnote 187, Endnote 188, Endnote 189 Oral contraceptive use and increases in the number of fullterm pregnancies may have protective effects.Endnote 52, Endnote 86, Endnote 190 Fertility rate in Canada has recently stabilized after a long-term decrease.Endnote 149 The stable prevalence in both oral contraceptive useEndnote 181 and fertility may partly explain the recent relatively stability of ovarian cancer incidence rate in females younger than 55.

A family history of ovarian cancer confers a 3- to 5-fold increased risk of the disease in most studies,^{Endnote 191, Endnote 192, Endnote 193} with 5% to 10% of ovarian cancers due to heritable risk.^{Endnote 187, Endnote 191, Endnote 192} The known susceptibility genes (e.g. BRCA1 and BRCA2) explain less than 40% of the excess risk of hereditary ovarian cancer.^{Endnote 191}

Potential links between ovarian cancer and lifestyle exist. IARC stated in 2009 that there is sufficient evidence that smoking causes ovarian cancer.^{Endnote 194} Overweight and obesity are moderately associated with ovarian cancer risk.^{Endnote 86} Vegetables and fruit appear to be inversely related to the risk.^{Endnote 86}