Cancer is an abnormal growth of cells in the human, which can grow in any part of the body (organs and on the skin). When this abnormal growth begins in the ovary (the female reproductive organ that produces the eggs), then can a woman develop ovarian cancer. This can spread to other parts of the body if it’s left untreated (metastatic ovarian cancer).

Ovarian cancer is a malignant tumour in one or both ovaries, thus starting in any of the three cells found in the ovary (epithelial cells, germinal cells and stromal cells). All these cells in the body go through their own life cycles – growing, dividing and being replaced; and also a programmed cell death when they no longer function properly or have their usefulness.

This type of women cancer was previously believed to only begin in the ovaries, but recent studies has suggested that many ovarian cancers can actually start in the cells in the distal end of the fallopian tubes. It can also spread from the ovaries to the diaphragm, the lining of the abdomen (peritoneum), and the sheet of fatty tissue that hangs inside the abdomen (omentum).

Ovarian cancer often goes undetected until it has spread within the pelvis and abdomen; making it becomes more difficult to treat. Early - stage ovarian cancer, in which the disease is confined to the ovary, is more likely to be treated successfully.

Although ovarian cancer may occur at any age, it is more common in patients older than 50 years, yet it only accounts for 3 percent of cancers in women worldwide. However, it is the fifth most common cause of cancer death in women behind lung, breast, colorectal, and pancreatic cancers.  There has been a decline of less than 1 percent in the incidence of ovarian cancer in the previous two decades, and the mortality rate is largely unchanged. The incidence of ovarian cancer and mortality rates increase with age.

The Ovaries

The ovaries are part of the female reproductive system, which also includes the fallopian tubes, uterus (womb), cervix (the neck of the uterus), vagina (birth canal) and vulva (external genitals).

The ovaries are two small, grape-shaped organs. They are found in the lower part of the abdomen (the pelvic cavity). There is one ovary on each side of the uterus, close to the end of the fallopian tubes. Each ovary is made up of:

• Epithelial Cells – found on the outside of the ovary in a layer known as the epithelium
• Germinal (germ) Cells – found inside the ovaries, these cells eventually mature into eggs (ova)
• Stromal Cells – form connective (supporting) tissue within the ovaries, and produce the female hormones oestrogen and progesterone.

Each month, the ovaries release an egg (ovum) in a process called ovulation. The egg travels down the fallopian tube into the uterus. If the egg is fertilised by a sperm, it will implant itself into the lining of the uterus and grow into a baby. If the egg is not fertilised by a sperm, the lining is shed and flows out of the body through the vagina. This flow is known as a woman's period (menstruation).

Oestrogen and progesterone cause ovulation and menstruation. As a woman gets older, the ovaries gradually produce less of these hormones. When the levels of oestrogen and progesterone fall low enough, a woman's periods will become irregular and finally stop. This is known as menopause. After menopause, it is no longer possible to conceive a child. The ovaries also become smaller.

Types of Ovarian Cancer

There are many types of ovarian cancer depending on the type of cell where the cancer begins thus determining the type of ovarian cancer. But there are three most common types of ovarian cancer, and they include:

Epithelial Tumors

This is a type of ovarian cancer that manifest in the thin layer of tissue that covers the outer surface of the ovaries. They are the most common and invasive, accounting between 85% - 90% of women with ovarian cancer. These tumors usually develops among women above the 50 years margin; and they can be benign (not cancer), borderline (low malignant), or malignant (cancer).

• Benign Epithelial Ovarian Tumors: Epithelial ovarian tumors are ovarian tumors which are benign, don’t spread and usually don’t lead to serious illness.
• Borderline Epithelial Tumors: When looked at in the lab, some ovarian epithelial tumors don’t clearly appear to be cancerous and are known as borderline epithelial ovarian cancer. The two most common types are atypical proliferative serous carcinoma and atypical proliferative mucinous carcinoma. These tumors were previously called tumors of low malignant potential (LMP tumors). These are different from typical ovarian cancers because they don’t grow into the supporting tissue of the ovary (called the ovarian stromal). If they do spread outside the ovary, for example, into the abdominal cavity (belly), they might grow on the lining of the abdomen but not into it.
• Malignant Epithelial Ovarian Tumors: Cancerous epithelial tumors are called carcinomas. About 85% to 90% of malignant ovarian cancers are epithelial ovarian carcinomas. These tumor cells have several features (when looked at in the lab) that can be used to classify epithelial ovarian carcinomas into different types. The serous type is by far the most common, and can include high grade and low grade tumors. The other main types include mucinous, endometrioid, and clear cell.

Stromal Tumors (Sex Cordstromal Tumors)

This is a rare cancer that begins in the ovarian tissue that produces the female hormones oestrogen and progesterone. They are usually diagnosed at an early stage than any other ovarian tumors. It usually occurs among women within the age 40 -50 years. About 1 percent of ovarian cancers are ovarian stromal tumor (women older than 50 years), but 5 percent of stromal tumor occur in young women below the age of 50 years.

Germ Cell Tumors

Germ cell tumors are rare ovarian cancers that tend to occur in younger women. They begin in the egg – producing cells in a woman, and also in sperms of the male organ. Most germ cell tumor is benign, yet there are some cancerous ones, thus causing life –threatening cases. Of all ovarian cancers cases, germ cell tumor cause less than 4%, bringing a survival case ratio of 9 out of 10 patients after diagnosis for at least 5 years.

Ovarian Cysts

Ovarian cysts are a collection of fluid that develops in or around the ovary. It is normally a part of ovulation, especially when the ovary releases an egg, causing mild symptom like bloating, and go away without any form of treatment. But they can be of a more concern the moment a lady might have stop ovulating (after menopause).

These cysts are usually benign, yet some few numbers can be cancerous.

Ovarian Cancer in Nigeria

Globally, ovarian cancer is the 7th commonest cancer in women; accounting for only 3.6% of various cancers diagnosed in women. It is the 3rd commonest genital tract malignancy after cancers of the cervix and uterus with over 1.5 million cases since the year 2012. It is equally the leading cause of genital cancer mortality in developed countries with estimated age standardized mortality rate of 5.0 per 100,000 women.

In Nigeria, ovarian cancer is the 7th commonest cancer in women and the 2nd commonest genital tract cancer after cervical cancer. It accounted for 2792 incident cases in 2018, which has increased to an estimated 6,302 cases in the year 2020; and with estimated age standardized incidence rate of 5.6 per 100,000 women.

It is also the 2nd leading cause of female genital cancer related deaths in the country with approximately 2063 deaths in 2018, a crude mortality rate of 2.9% and estimated age standardized mortality rate of 4.4 per 100,000 women.

Lack of knowledge of a premalignant stage, the absence of a reliable screening tool, and inaccessibility of the ovary to screening further complicate the problem. Nigeria shares in the universal observation of late presentation for ovarian cancer as more than 75% of cases are presently in advanced stages, but the challenges in management including lack of organized cancer care worsen its prognosis.

[Next Article on Ovarian Cancer: Clinical Presentation of Ovarian Cancer]