Women delaying or not having children may be contributing to a sharp rise in womb cancer, experts warn.
Rates have risen by a quarter in the last decade and there are now 8,700 new cases a year in the UK. But the risk of developing the illness is a third higher in women who have never had children.
This is because they are more exposed during their lives to the hormone oestrogen, which may trigger tumour growth.
Changes in patterns of motherhood are among several modern lifestyle factors contributing to a significant rise in all types of cancer in the last few decades.
A report released today by Cancer Research UK shows that rates of the different types of the illness have increased by 12 per cent since the 1990s. The rise is mainly due to the ageing population.
But the charity also said lifestyle reasons such as obesity, smoking, drinking and not having children are playing a part. Further analysis shows that rates are increasing faster in the particular cancers most linked to modern lifestyles. Liver cancer rates have increased by 59 per cent in a decade, partly due to excessive drinking and being overweight. Womb cancer is now the fourth most common cancer in women after breast, bowel and lung.
Breast cancer rates have risen by eight per cent in 10 years, from 152 per 100,000 to 165 per 100,000. The risk is higher in women who have not had children and have never breast-fed, and it is also linked to smoking, obesity and alcohol.
Fiona Osgun, Cancer Research UK's health information officer, said: "Having fewer children, or having them later on in life, is linked to an increased risk of breast and some other cancers.
"But there are plenty of things we have more control over - such as not smoking, keeping a healthy weight, eating a healthy balanced diet, being physically active, drinking less alcohol and staying safe in the sun - that can help lower the risk of cancer."
Women's oestrogen levels fall during pregnancy and breastfeeding, and scientists believe this hormone may cause tumours to grow.
Levels of progesterone increase during pregnancy - and it is believed this hormone may protect against cancer. As many as one in five women aged 45 are childless and the numbers are almost twice as high compared to the 1940s.
Professor Peter Johnson, Cancer Research UK's chief clinician, said: "People often think cancer is down to their genes or just bad luck. Although genes do play a role there are still many things people can do to reduce their cancer risk. The most important is to not smoke.
"Most people know smoking causes lung cancer, but it's also linked to at least 13 other types.
"We also know that maintaining a healthy body weight, exercising and eating a healthy balanced diet is important. There is no guarantee against cancer but there are things we can do to make us less likely to get it, and things that the Government can do help us to make the right choices and protect future generations."
The analysis shows that rates of cancer have increased by 12 per cent from 540 per 100,000 in 1993-1995 to 603 per 100,000 in 2011-2013.
But the charity also pointed out that survival rates had doubled in the past 40 years thanks to earlier diagnosis, screening programmes and improved treatment. It hopes that within the next 20 years three-quarters of cancer patients will be cured, up from half currently.
Only yesterday US scientists announced a new therapy for leukaemia that had enabled 90 per cent of patients to go back into remission.
Nick Ormiston-Smith, Cancer Research UK's head of statistical information, said: "People are living longer so more people are getting cancer. But the good news is more people are surviving their cancer."
NHS England said: 'More people are surviving cancer than ever before, but we know we can do more to diagnose cancers earlier, treat them more effectively and prevent them in the first place.'