Ovarian cancer was the fourth most common cancer for women in Ireland, accounting for 4.6% of all malignant neoplasms, excluding non-melanoma skin cancer (Table 17.1). The average number of new cases diagnosed each year was 479. During 1995-2007, there was little change in the number of new cases diagnosed per year in RoI while the numbers decreased slightly in NI.

The risk of developing ovarian cancer up to the age of 74 was 1 in 71 and was similar in NI and RoI. At the end of 2008, 1,441 women aged under 65 and 994 women aged 65 and over were alive up to 15 years after their cancer diagnosis.

Table 17.1 Summary information for ovarian cancer in Ireland, 1995-2007

The age distribution of ovarian cancer at diagnosis was more uniform than for most other cancers (Figure 17.1). Approximately 18% of cases presented under 50 years of age, 21% between 50 and 59, 25% between 60 and 69 and 23% between 70 and 79; the remainder (13%) presented at 80 years or over. There was a similar age pattern in RoI and NI.

Figure 17.1 Age distribution of ovarian cancer cases in Ireland, 1995-2007

In 2008, estimated rates of ovarian cancer were high in the UK, RoI and NI and also in Poland and the Czech Republic (Figure 17.2). Rates of the disease were lowest in Portugal, followed by Japan, Australia and Canada. Differences in the coding of borderline ovarian cancers by cancer registries may account for some of the international differences in incidence rate.

Figure 17.2 Estimated incidence rate per 100,000 in 2008 for selected developed countries compared to 2005-2007 incidence rate for RoI and NI: ovarian cancer

Source: GLOBOCAN 2008 (Ferlay et al., 2008) (excluding RoI and NI data, which is derived from Cancer Registry data for 2005-2007)

Table 17.2 Risk factors for ovarian cancer, by direction of association and strength of evidence

Family history of the disease is the most important risk factor for ovarian cancer. Women with at least one affected first degree relative have a three-fold increased risk of developing ovarian cancer themselves. Together with breast cancer, ovarian cancer is a component of several autosomal dominant cancer syndromes, most notably the BRCA1 and BRCA2 mutation syndromes. Women who have mutations in the BRCA1 or BRCA2 genes have a high chance of developing ovarian cancer over their lifetime (39% risk for BRCA1 mutation carriers and 11% for BRCA2 mutation carriers up to the age of 70; Antoniou et al., 2003).

Endogenous and exogenous oestrogens play a key role in the aetiology of ovarian cancer. Not having children (nulliparity) is associated with increased risk and, by contrast, each additional child confers a 20% reduction in risk (Riman et al., 2004). Women who have used fertility drugs may also have raised risk, especially if they remain nulligravid. Risk is reduced in women who have had bilateral tubal ligation (their fallopian tubes “tied”) or hysterectomy with ovarian conservation. In terms of exogenous hormones, use of hormone replacement therapy, particularly oestrogen-only formulations, is clearly related to increased risk, although formulations which include progestin are associated with only a modest risk. Women who have used combined oestrogen-progestogen oral contraceptives have decreased risk. Protection increases with increasing duration of use, and the reduction in risk persists for more than 30 years after use has ceased. Breastfeeding has also been associated with lower risk of ovarian cancer, but uncertainties remain in the evidence.

Risk of ovarian cancer is raised in taller women, but tallness in itself is unlikely to be a causal factor; it is most likely a marker for factors relating to promoters of growth in childhood (World Cancer Research Fund / American Institute of Cancer Research, 2007).

Several lifestyle factors have been related to ovarian cancer risk, but most of the associations remain somewhat uncertain. The exception is smoking, which is causally related to mucinous ovarian tumours, but not to other tumour types (Jordan et al., 2006). Higher intake of non-starchy vegetables may be associated with reduced risk, but this category includes a wide and disparate group of vegetables with many different plant food constituents (e.g. fibre, folate, flavonoids) and the contributions of the different constituents have not been unravelled (World Cancer Research Fund / American Institute of Cancer Research, 2007). There may be a modest (approximately 20%) reduction in risk among women with the highest, versus those with the lowest, levels of recreational physical activity. Body fatness and/or obesity may also be related to increased risk.

Map 17.1 Ovarian cancer, smoothed relative risks