The causes of testicular cancer are not fully understood.

However, we do know about several things that increase your risk of developing the condition.

Increased risk

Some risk factors for testicular cancer are outlined below.

Undescended testicles

Undescended testicles is the most significant risk factor.

When male babies grow in the womb, their testicles develop inside their abdomen. The testicles then normally move down into the scrotum when the baby is born or during their first year of life.

However, for some children, the testicles fail to descend. The medical name for undescended testicles is cryptorchidism. 

Surgery is usually required to move the testicles down. If you have had surgery to move your testicles down into your scrotum, your risk of developing testicular cancer may be increased.

One study found that if surgery is performed before the child is 13 years of age, their risk of later developing testicular cancer is approximately double that of the rest of the population. However, if the operation is carried out after the boy is 13 years of age, the risk of developing testicular cancer is five times greater than that of the rest of the population.

Previous testicular cancer

Men who have previously been diagnosed with testicular cancer are 12 times more likely to develop testicular cancer in the other testicle.

For this reason, it is important to attend follow-up appointments if you have previously been diagnosed with testicular cancer.

Age and race

Unlike most other types of cancer, testicular cancer is more common in young and middle-aged men with an average of 85% of cases diagnosed in men aged 15-49. Men aged 30-34 are most likely to be diagnosed with testicular cancer.

Testicular cancer is more common in white men than other ethnic groups. It is also more common in Northern and Western Europe compared with other parts of the world.

Family history

Having a close relative with a history of testicular cancer increases your risk of developing it.

If your father had testicular cancer, you are four to six times more likely to develop it than a person with no family history of the condition. If your brother had testicular cancer, you are eight to 10 times more likely to develop it (having an identical twin with testicular cancer means that you are 75 times more likely to develop it).

The fact that testicular cancer appears to run in families has led researchers to speculate that there may be one or more genetic mutations (abnormal changes to the instructions that control cell activity) that make a person more likely to develop testicular cancer.

A promising piece of research carried out in 2009 identified mutations in two genes (known as the KITLG and SPRY4 genes) that appear to increase the risk of a person developing testicular cancer.

Endocrine disruptors

Examples of endocrine disruptors include:

• some types of pesticide
• polychlorinated biphenyls (PCBs), chemical compounds used as a coolant
• dibutyl phthalate, a chemical used to manufacture cosmetics, such as nail polish

In most countries, including the UK, many endocrine disruptors, such as PCBs, have been withdrawn as a result of their link to health problems. However, there is a concern that exposure to endocrine disruptors may still occur due to contamination of the food chain.

However, there is not yet enough evidence to prove a definite link between indirect exposure to low levels of endocrine disruptors and health problems. Indirect exposure is the type of exposure that would occur if the food chain was contaminated.

Infertility

Men who are infertile are three times more likely to develop testicular cancer than fertile men.

The reasons for this are not clear.

Smoking

Research has found that long-term smokers (people who have been smoking a pack of 20 cigarettes a day for 12 years or 10 cigarettes a day for 24 years) are twice as likely to develop testicular cancer than non-smokers. 

HIV and AIDS

Studies show that men with HIV or AIDS have an increased risk of testicular cancer.

Height

A study that was carried out in 2008 found that a man’s height affects his chances of developing testicular cancer.

Men who are 190-194cm (6.1-6.3ft) tall are twice as likely to develop testicular cancer than men of average height. Very tall men, who are 195cm (6.4 ft) or above, are three times more likely to develop testicular cancer than men of average height.

Being shorter, less than 170cm (5.6ft) tall, decreases your risk of getting testicular cancer by around 20%.

Researchers who conducted the study think the link between height and cancer risk may be caused by diet. Taller children often require a higher-calorie diet as they are growing up, and it may be the effects of such a diet that leads to the increase in cancer risk.