Different types of ovarian cancer have different causes

The National Cancer Research Institute (NCRI)

The more children a woman has or whether a woman has had her fallopian tubes cut lowers the risk of different types of ovarian cancer to different levels, according to new research* presented at the 2015 National Cancer Research Institute (NCRI) Cancer Conference today (Tuesday).

"Our results are really interesting, because they show that the associations with known risk factors for ovarian cancer, such as childbirth and fertility, vary between the different tumour types." - Dr Kezia Gaitskell, lead researcher.

Data was collected from more than 8000 women with ovarian cancer as part of the UK Million Women Study.

Researchers then examined the risk of the four most common types of ovarian cancer – serous, mucinous, endometrioid and clear cell tumours – in women with different childbearing patterns.

For ovarian cancer overall, women with one child had about a 20 per cent reduction in risk compared to women without children, and about a 40 cent reduction of endometrioid and clear cell tumours.

Each additional birth then offered an estimated eight per cent reduction in the overall risk of ovarian cancer.

Researchers also compared risk between those women who had surgery to cut or clip their fallopian tubes with those who had not. This procedure – known as tubal ligation or sterilisation – is a surgical procedure for permanent contraception.

Women who had had this surgery had a 20 per cent lower overall risk of ovarian cancer. The risk was about 20 per cent lower for high-grade serous tumours – the most common type of ovarian cancer – and about halved for endometrioid and clear cell tumours.

Dr Kezia Gaitskell, Cancer Research UK funded lead researcher and pathologist based at the Cancer Epidemiology Unit, University of Oxford, said: “In the last few years, our understanding of ovarian cancer has been revolutionised by research showing that many cases may not in fact come from the ovaries. For example, many high-grade serous tumours - the most common type - seem to start in the fallopian tubes, while some endometrioid and clear cell tumours may develop from endometriosis.

“We think that the significant reduction in risk among women with one child compared to women without children is likely to be related to infertility, as there are some conditions - such as endometriosis - that may make it harder for a woman to become pregnant, and which may also increase her risk of these specific types of ovarian cancer.

“For the reduced risk seen among women with tubal ligation - it could be that tubal ligation acts as a barrier to help prevent the abnormal cells that might cause these tumours passing through the fallopian tubes to the ovaries. Our results are really interesting, because they show that the associations with known risk factors for ovarian cancer, such as childbirth and fertility, vary between the different tumour types.”

Professor Charles Swanton, Chair of the 2015 NCRI Cancer Conference, said: “We’ve known for some time that the number of children a woman has, and her use of contraception, can influence her risk of ovarian cancer, so this research provides important further detail about different types of the disease.

“Ovarian cancer – like many other cancers – is not one disease, but different diseases that are grouped together because of where they start. It’s important to know what affects the risk of different types of ovarian cancer and what factors impact this. We now need to understand the mechanisms behind these findings to develop some way to extend this lower risk to all women, regardless of how many children they have.”

ENDS

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Notes to Editor

*http://abstracts.ncri.org.uk/abstract/childbearing-patterns-and-ovarian-cancer-in-the-million-women-study-variation-by-histological-subtype/

The researchers have made the following calculations for the absolute risk of ovarian cancer relating to how many children a woman has, or if she has had her fallopian tubes cut.

PARITY (How many children a woman has)

 

Cases

Incidence rate of ovarian cancer per 100,000 woman-years

All ovarian cancer

8135

51.4

Women without children

1198

70.8

Women with one child

1218

54.9

Women with children (1 or more)

6937

49.0

 

 

 

Endometrioid and clear cell tumours (together)

995

6.3

Women without children

217

12.8

Women with one child

155

7.0

Women with children (1 or more)

778

5.5

 

 

 

TUBAL LIGATION (surgery to cut or clip the fallopian tubes)

 

Cases

Incidence rate of ovarian cancer per 100,000 woman-years

All ovarian cancer

8035

51.3

Women without tubal ligation

6693

54.6

Women with tubal ligation

1342

39.6

 

 

 

Endometrioid and clear cell tumours (together)

990

6.3

Women without tubal ligation

890

7.3

Women with tubal ligation

100

3.0

 

 

  • Around 7000 women are diagnosed with ovarian cancer every year in the UK - Based on the number of cases of ovarian cancer (ICD10 C56-C57.4) diagnosed in the UK in 2012
  • In the UK, the lifetime risk of developing ovarian cancer is 1 in 51 for women. Lifetime risk of being diagnosed with ovarian cancer (ICD10 C56-C57). Calculated by Cancer Research UK Stats Team using the AMP method. Based on 2010 data.

For the latest statistics on ovarian cancer visit http://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/ovarian-cancer

Ovarian cancers are classified depending on the type of cells and where they start growing from. Epithelial ovarian cancer is the most common form of the disease, responsible for nine out of ten cases, and there are various sub-types of epithelial ovarian cancers – including serous, endometrioid, clear cell and mucinous tumours.

These results come from the Million Women Study, which is funded by Cancer Research UK and the Medical Research Council.

Tubal ligation is a surgical procedure for sterilisation in which a woman's fallopian tubes are clamped and blocked, or severed and sealed. The aim is to prevent eggs from reaching the uterus for implantation. Tubal ligation is considered a permanent method of sterilisation and birth control. It is also known as having your "tubes tied".

http://www.nhs.uk/conditions/contraception-guide/pages/female-sterilisation.aspx#female

Results of the work on tubal ligation are in press at the International Journal of Cancer:

http://onlinelibrary.wiley.com/doi/10.1002/ijc.29856/abstract