Women diagnosed with breast cancer under the age of 35 face a higher risk of it spreading, according to the first global study of its kind.

Breast cancer is the most common form of cancer, with 2.3 million people diagnosed every year. Survival rates are generally good, which is largely because of screening, early diagnosis and improved treatment.

However, until now, little has been known about the risk of secondary breast cancer, where the disease spreads to other parts of the body and becomes incurable.

A meta analysis of more than 400 studies has found the risk of breast cancer spreading to another part of the body ranges from 6% to 22%. The results of the study are being presented at the sixth International Consensus Conference for Advanced Breast Cancer .

The findings also suggest certain women face a higher risk, including those diagnosed with breast cancer under the age of 35, those with larger tumours when initially diagnosed and those with specific types of the disease, for example luminal B.

Kotryna Temcinaite, senior research communications manager at the charity Breast Cancer Now, said the analysis “provides helpful insight into who is most at risk”.

“About 1,000 women in the UK die each month from incurable secondary breast cancer,” she said. “We desperately need to learn more about this devastating disease so that we can find new ways to improve treatment, care and support for people living with it, and for those living in fear of a diagnosis.

“The data shows that people diagnosed with primary breast cancer aged 35 years or younger have the greatest chance of developing secondary breast cancer. The study also highlights that the size of the tumour, the type of breast cancer and the length of time since primary diagnosis can impact a person’s risk.

“Secondary breast cancer can develop many years after an initial cancer diagnosis, so it’s vital that we understand it better and find new ways to prevent it.”

For the study, researchers analysed data on tens of thousands of women across more than 400 studies from North and South America, Europe, Africa, Asia and Oceania.

The analysis suggests the overall risk of metastasis for most breast cancer patients is between 6% and 22%. Researchers say the range is broad because the risk varies significantly depending on a whole range of different factors.

For example, women first diagnosed under the age of 35 have a 12.7% to 38% risk of their breast cancer coming back and spreading to other parts of the body, while women aged 50 years or older have a risk of 3.7% to 28.6%.

“This may be because younger women have a more aggressive form of breast cancer or because they are being diagnosed at a later stage,” said the presenter of the study, Dr Eileen Morgan, of the International Agency for Research on Cancer (IARC).

“Breast cancer is the most common form of cancer in the world,” she said. “Most women are diagnosed when their cancer is confined to the breast or has only spread to nearby tissue. But in some women, the cancer will grow and spread to other parts of the body or come back in a different part of the body several years after the end of their initial treatment.

“At this point the cancer becomes much harder to treat and the risk of dying is higher. However, we don’t really know how many people develop metastatic breast cancer because cancer registries have not been routinely collecting this data.”

The study also found women with specific types of breast cancer appeared to have a higher risk of it spreading, for example those with a type of cancer called luminal B.

Those with this form had a 4.2% to 35.5% risk of it spreading compared with 2.3% to 11.8% risk in women diagnosed with luminal A cancer.

Dr Shani Paluch-Shimon, a member of the conference’s scientific committee and director of the breast unit at Hadassah University hospital in Israel, who was not involved with the research, said the findings were “vital” for patients and doctors.