In adult women the majority of growths which occur in the ovary are benign (non-cancerous). About 7 out of 10 ovarian tumours in women over 20 are benign whilst only 3 out of 10 are cancers.

Of the cancerous growths about 5-10% will turn out to be a 'borderline tumour'. This means that when the tumour is looked at under the microscope there are cells which are probably cancerous in appearance but they will not actually have begun to spread into or damage the surrounding normal tissue in that ovary. As a result there is some uncertainty as to whether these growths should really be called cancers hence the name of borderline tumours, since they are on the border between benign and malignant (cancerous) growths.

The average age of women who develop borderline ovarian tumours is 40, (and some occur in much younger women) about 20 years younger than the average age for cancers of the ovary. By the time these tumours are diagnosed they will often have reached a size of 7 to 10 cm across (3 to 4 inches) and in around about half the women there will be tumours on both ovaries.

The treatment is an operation to remove the growth, or growths. In women who have passed the menopause this will usually be a removal of both ovaries, the fallopian tubes and the womb (uterus). In younger women, who are still hoping to have children, wherever possible the surgery will involve removal of the affected ovary and its fallopian tube only, or part of the ovary, so that fertility can be preserved.

Usually surgery results in a complete cure of these growths and there is no need for any additional treatments like chemotherapy or radiotherapy. Women who have had a borderline ovarian tumour do need careful follow up including regular examination, blood tests and scans, to make sure that any recurrence can be detected at an early stage.