Ovarian cancer is any cancerous growth that may occur in different parts of the ovary. The majority of ovarian cancers arise from the epithelium (outer lining) of the ovary. According to the American Cancer Society it is the 8th most common cancer among women in the USA (excluding non-melanoma skin cancers). In the UK ovarian cancer is the fifth most common cancer among females, after breast cancer, bowel cancer, lung cancer and uterine cancer (cancer of the uterus).
Approximately 21,000 women in the USA and 5,500 women in the UK are diagnosed with ovarian cancer each year. Worldwide, around 140,000 women die of ovarian cancer every year.
Tragically, the overall five year survival rate is only 46 per cent in most developed countries (it is lower for more advanced stages). However, according to the National Cancer Institute, if diagnosis is made early, before the tumor has spread, the five year survival rate is nearer 93 per cent. In 2009 scientists in the US said that current tests for diagnosing ovarian cancer are not good enough .
What are the ovaries?
The ovary is the female gonad, while the testis is the male gonad. A gonad is a reproductive gland that produces germ cells (gametes). A male sperm is a gamete, and a female egg is also a gamete. Each human gamete has 23 chromosomes, half the number of chromosomes contained in most types of human body cells.
The ovary, also known as the egg sac, is one of a pair of reproductive glands in women. The ovaries are located at either side of the uterus (womb), in the pelvis. Each ovary is about the size and shape of an almond. The ovaries produce ova (eggs) and female hormones, such as estrogen and progesterone. These hormones regulate the menstrual cycle, pregnancy, and control the development of female characteristics, such as body shape, body hair, breasts, etc.
During the female menstrual cycle, which lasts about one month, one egg is released from one of the two ovaries - the egg travels through the fallopian tube and into the uterus. This is known as ovulation.
Cancer of the ovary can spread to other parts of the reproductive system as well as surrounding areas, such as the stomach, vagina and uterus. Ovarian cancer more commonly occurs in women aged 65 or over, but can affect women of any age.
What is cancer?
Cancer is a class of diseases characterized by out-of-control cell growth. There are over 100 different types of cancer that occur in various parts of the body - each is classified by the type of cell that is initially affected.
Usually our cells divide (multiply, form new ones) only when old and dying ones need to be replaced. However, the controls that regulate when a cell divides as well as when a cell should die sometimes become faulty. This may result in cells not dying when they should, while additional cells are still being added - an uncontrolled accumulation of cells. Eventually a mass of cells is formed - a tumor.
Malignant and benign tumors
Tumors that stay in one place and demonstrate limited growth are usually considered to be benign. Malignant, or more dangerous tumors emerge when two things occur:
- Invasion - the cancerous cell manages to move throughout the body using the blood or lymphatic systems, destroying healthy tissue - this process is called invasion.
- Angiogenesis - the cancerous cells manage to divide and grow, making new blood vessels to feed themselves.
When a tumor manages to spread to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a serious condition that is extremely hard to treat.
Three main types of ovarian cancers (tumors)
Epithelial ovarian cancer is by far the most common form of ovarian cancer. Germ cell and stromal ovarian cancers are much less common. Ovarian cancer can also result from a cancer somewhere else in the body that has spread:
- Epithelial ovarian cancer (epithelial ovarian tumors) - derived from cells on the surface of the ovary. It occurs mainly in adults.
- Germ cell ovarian cancer (germ cell ovarian tumors) - derived from the egg-producing cells within the body of the ovary. This rare type of cancer more commonly affects children and teenage girls.
- Stromal ovarian cancer (sex cord stromal tumors) - develops within the cells that hold the ovaries together.
- Cancers from other organs in the body can spread to the ovaries - metastatic cancers - a metastatic cancer is one that spreads from where it first arose as a primary tumor to other locations in the body.
What are the symptoms of ovarian cancer?In the early stages, ovarian cancer usually has vague symptoms which are not easy to recognize. In fact, doctors used to think that ovarian cancer had no symptoms (unfortunately, many still do). Even though healthcare professionals are much better at identifying ovarian cancer symptoms these days, patients often attribute their symptoms to other conditions, such as pre-menstrual syndrome, irritable bowel syndrome, or a temporary bladder problem.
The main difference between ovarian cancer and other possible disorders is the persistence and gradual worsening of symptoms. While most digestive disorders have fluctuating symptoms, those of ovarian cancer are more constant and steadily advancing.
The following are examples of possible early symptoms of ovarian cancer:
- Pain in the pelvis
- Pain on the lower side of the body
- Pain in the lower stomach
- Back pain
- Indigestion or heartburn
- Feeling full rapidly when eating
- More frequent and urgent urination
- Pain during sexual intercourse
- Changes in bowel habits, such as constipation
- Weight loss
- Fatigue (tiredness)
- Loss of appetite
If you experience bloating, pressure or pain in the abdomen or pelvis that persists for more than a few weeks you should see your doctor immediately. If you have already been to the doctor and ovarian cancer was not diagnosed, but treatment is not relieving symptoms, either see your doctor again or get a second opinion. It is important that the evaluation includes a pelvic examination.
People with close family members who have/had ovarian or breast cancer should see a doctor who is trained to detect ovarian cancer.
What are the causes of ovarian cancer?
Although we know that ovarian cancer, like many other cancers, is caused by cells dividing and multiplying in an unordered way, nobody completely understands why cancer of the ovary occurs. We know that the following risk factors are linked to a higher chance of developing the disease:
Most women who develop ovarian cancer do not have an inherited gene mutation. Women with close relatives who have/had ovarian cancer, as well as breast cancer, have a higher risk of developing ovarian cancer compared to other women. There are two genes - BRCA1 and BRCA2 - which significantly raise the risk. The BRCA1 and BRCA2 genes also raise the risk of breast cancer. Those genes are inherited. The BRCA1 gene is estimated to increase ovarian cancer risk by 35% to 70%, and the BRCA2 by 10% to 30%. People of Ashkenazi Jewish descent are at particularly high risk of carrying these types of gene mutations.
Genetic screening can determine whether somebody carries the BRCA1 and/or BRCA2 genes. Although a test for gene mutations known to significantly increase the risk of hereditary breast or ovarian cancer has been available for more than a decade, a study by researchers from Massachusetts General Hospital found that few women with family histories of these cancers are even discussing genetic testing with their physicians or other health care providers.
After eight years of searching, an international team of scientists found that a single nucleotide polymorphisms (SNP) on chromosome 9 that is uniquely linked to ovarian cancer. The scientists estimated that women carrying that particular version of the SNP on both copies of chromosome 9 have a 40 per cent higher lifetime risk of developing ovarian cancer than women who do not carry it on either copy of chromosome 9, while women with only one copy of the variant have a 20 per cent higher lifetime risk of developing ovarian cancer than women who have none.
In March 2013, scientists from the University of Cambridge and the Institute of Cancer research announced that they had identified over 80 genome regions that can increase a human's risk of developing ovarian, breast and prostate cancers.
The majority of ovarian cancers occur in women over 65 years of age. A higher percentage of post-menopausal women develop ovarian cancer compared to pre-menopausal women.
High number of total lifetime ovulations
There is a link between the total number of ovulations during a woman's life and the risk of ovarian cancer. Four principal factors influence the total:
- Never having been pregnant - women who have never become pregnant have a higher risk of developing ovarian cancer compared to women who have became pregnant. The more times a woman has become pregnant the lower her risk is.
- Never having taken the contraceptive pill - women who have never been on the contraceptive pill have a higher risk of developing ovarian cancer compared to women who have. Taking the Pill for 15 years halves the risk of ovarian cancer, a study by the Collaborative Group on Epidemiological Studies of Ovarian Cancer found.
- Early start of menstruation (early menarche) - women who started their periods at an early age have a higher risk of developing ovarian cancer.
- Late start of menopause - women whose menopause started at a later age than average have a higher risk of developing ovarian cancer.
Some gynecologic surgeries may reduce the risk
Women who have had their fallopian tubes tied (tubal ligation) are estimated to have a 67% lower risk of ovarian cancer. A hysterectomy is said to reduce the risk by about one third.
Infertility or fertility treatment
Some studies have found a link between infertility treatment and a higher risk of ovarian cancer. Nobody is yet sure whether the risk is linked to infertility treatment, just infertility itself, or both. A Danish study published in the peer-reviewed British Medical Journal concluded that the use of fertility drugs does not increase a woman's risk of developing ovarian cancer. The study involved 54,362 women with infertility problems referred to all Danish fertility clinics between 1963 and 1998.
Women who have been diagnosed with breast cancer have a higher risk of developing ovarian cancer.
HRT (Hormone replacement therapy)
HRT slightly increases a women's risk of developing ovarian cancer. Experts say the risk grows the longer the HRT continues, and returns to normal as soon as treatment stops. Danish scientists reported that compared with women who have never taken hormone therapy, those who currently take it or who have taken it in the past are at increased risk of ovarian cancer, regardless of the duration of use.
A UK study that was published in the peer-reviewed medical journal The Lancet suggested that between 1991 and 2005, an extra 1,000 women in the UK died of ovarian cancer because they were on Hormone Replacement Therapy.
Being obese or overweight increases the risk of developing many cancers. The more overweight you are, the higher the risk. Several studies have also shown that obese cancer patients are more likely to have faster advancing ones compared to cancer patients of normal weight. Obese older women who have never used hormone replacement therapy have nearly twice the risk of their normal weight peers of developing ovarian cancer, according to a study by the researchers at the National Cancer Institute.
New research suggests that women who are overweight or obese are more likely to develop ovarian cancer, compared with women of a healthy weight. Being overweight or obese 'a risk factor' for ovarian cancer. Investigators from the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research conducted the study as part of the WCRF's Continuous Update Project.
Women who develop endometriosis have an approximately 30% higher risk of developing ovarian cancer compared to other women. Endometriosis is a condition in which cells that are normally found inside the uterus (endometrial cells) are found growing outside of the uterus. Danazol, a medication used to treat endometriosis has been linked to ovarian cancer risk.
Women who work shifts are more likely to develop ovarian cancer than other females, scientists from the Fred Hutchinson Cancer Research Center in Seattle, USA, revealed in Occupational and Environmental Medicine.
In the same issue of the journal, other authors explained in an Accompanying Commentary that "night-type people" ("owls") who work shifts are less likely to have a higher ovarian cancer risk compared to "morning types" ("larks").
On the next page we look at how ovarian cancer is diagnosed, the 4 stages of ovarian cancer and the available treatment options.