1Epidemiology of epithelial ovarian cancer
Introduction
Globally, 240,000 women are diagnosed with ovarian cancer every year and, with five-year survival below 45%, it is responsible for 150,00 deaths making it the 7th most common cancer and 8th most common cause of cancer death among women [1]. Figure 1A shows that age-standardised incidence rates are highest in northern and central/eastern Europe, intermediate in north America, Australia and western Europe and lowest in Asia and Africa. Rates have been decreasing in most high incidence countries but increasing in many low incidence countries (Figure 1B) thus the differences today are less marked than 30 years ago [2]. Rates also vary by ethnicity within countries such that in the United States, rates in non-Hispanic white women are approximately 30% higher than African-American and Asian women and 12% higher than Hispanic women [3].
Ovarian cancer is rare in women under 40 years of age and most cancers in this age group are germ cell tumours. Above age 40, more than 90% are epithelial tumours and the risk increases with age, peaking in the late 70s. Despite being classified as ovarian, a high proportion of high-grade serous cancers are now thought to originate from the fallopian tube. In the following discussion the term ‘ovarian cancer’ refers to epithelial cancers that arise in the ovary or fallopian tube as well as the histologically similar primary peritoneal cancers.
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Risk factors
It is well established that women with a family history of ovarian cancer are themselves at higher risk of the disease. The risk for women with one affected first-degree relative is about three times that for women with no affected relatives [4], and even higher for those whose relative was diagnosed below the age of 50 [5]. A high proportion of hereditary cancers are due to mutations in the BRCA genes, however BRCA mutations are also common among women with ovarian cancer who do not have a
Theories of carcinogenesis
The relationships described above have led to a number of theories about the mechanisms by which ovarian cancer develops. While the ovarian surface epithelium was thought to be the origin of epithelial ovarian cancers when these theories were developed, most of the processes they invoke also apply to the fallopian tube epithelium and so remain relevant.
Most commonly cited is the incessant ovulation theory which suggests that recurrent ovulation with repeated breakdown and repair of the ovarian
Opportunities for prevention
Unfortunately, many of the factors known to influence a woman's risk of ovarian cancer (Table 1) are not amenable to modification or, like pregnancy and OC use, cannot be promoted for cancer prevention. Furthermore, the factors that can be modified such as smoking, obesity and use of MHT have a small effect and/or only influence risk of some histotypes. Accordingly, an Australian study found that only 7% of ovarian cancers could be attributed to modifiable factors and thus potentially
Survival
We know much less about the influence of environmental factors on survival after a diagnosis of ovarian cancer. Obese women may have poorer survival than their normal weight counterparts, perhaps, in part, due to the practice of dose-capping whereby obese women are not given the full chemotherapy dose for their body-size because of toxicity concerns [92]. A recent pooled analysis suggested women who were sedentary prior to diagnosis had worse outcomes [93] and others have reported benefits for
Summary
Ovarian cancer remains a significant cause of morbidity and mortality globally with rising rates in many low and middle income countries and increasing case numbers in high income countries because of population aging. Five-year relative survival is below 45% and, unlike other common cancer types, the proportion of women who die from their disease has not improved substantially over time. There are several well-established risk and protective factors for epithelial ovarian cancer; most relate
Conflict of interest statement
None.
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