All young women under the age of 35 years who have breast cancer should be regarded as high risk patients and offered chemotherapy after surgery, say researchers.

Breast cancer is usually treated with surgery; a lumpectomy to remove the tumour or a mastectomy to remove all the breast tissue.

The patient may also be recommended radiation treatment to kill cells left over from the surgery, or chemotherapy if the disease has spread beyond the breast, or both.

A team of Danish scientists studied the treatment and outcome of 10,356 women with breast cancer who were younger than 50 at the time of their diagnosis.

They found that overall young women who were diagnosed with "low risk" breast cancers and who did not receive a form of chemotherapy known as adjuvant cytotoxic treatment had a significantly increased risk of dying compared to middle-aged women with "low risk" breast cancer.

According to the researchers from the Danish Epidemiology Science Centre, the younger the woman at diagnosis, the greater the risk.

Women under the age of the 35 who had not received adjuvant treatment were more than twice as likely to die as women aged 45 to 49 at diagnosis.

The researchers found that if women had received adjuvant therapy, age ceased to be a factor on their long-term outlook.

They warn that their results cannot be taken as direct evidence that young patients with low risk disease will benefit from adjuvant therapy.

However, they are confident that low risk tumours will respond well to such treatment.

Time is precious

Lead researcher Professor Mads Melbye said: "Only a small group of women develop breast cancer under the age of 35, but they tend to be young mothers and to them time is precious."

Dr Kate Law, head of clinical programmes for the Cancer Research Campaign, said it was well known that tumours tended to be more aggressive among younger people.

She said UK national guidelines suggested women under 50 suffering from breast cancer should be treated with chemotherapy.

However, she said the guidance was not strongly worded.

Dr Law said: "It would be good if this research got out among people treating women with breast cancer, so it could focus their attention."

Younger patients tend to have a more advanced cancer when they are diagnosed because their breasts are denser and small tumours are more difficult to detect than in older women.

Because the disease is usually more aggressive in young women it is also more likely to have spread beyond the breast into the lymphatic system.

Breast cancer is the most common cancer in women in many developed countries. It affects about one in 10 women and occurs most often in women over 50.