Female survivors of breast cancer living in the most deprived areas have a 35% higher risk of developing second, unrelated cancers, compared with those from the most affluent areas, research shows.

Breast cancer is the most commonly diagnosed cancer in the UK, with about 56,000 people being told they have it each year. Improved diagnosis and treatments mean that five-year survival rates are now 86% in England.

People who survive breast cancer have a greater likelihood of second primary (unrelated) cancer, but until now the exact risk has not been clear.

A team of researchers led by the University of Cambridge analysed NHS data from almost 600,000 patients in England and found, compared with the general female population, women who had survived breast cancer had an increased risk of developing 12 other primary cancers.

They had double the risk of developing cancer in the unaffected (contralateral) breast, an 87% higher risk of endometrial cancer, a 58% increased likelihood of myeloid leukaemia and a 25% higher risk of ovarian cancer.

The study, published in Lancet Regional Health – Europe, found that the risk of second primary cancers was higher in people living in areas of greater socioeconomic deprivation.

Compared with the most affluent, the least well-off female survivors of breast cancer had a 166% greater chance of developing lung cancer, a 78% higher risk of stomach cancer, more than 50% increased risk of bladder and oesophagus cancers, 48% higher risk of head and neck cancer and 43% increased risk of kidney cancer.

Overall, those from the most deprived areas had a 35% higher risk of a second non-breast cancer.

This may be because risk factors such as smoking, obesity and alcohol consumption are more common among more deprived groups. A 2023 study found that deprivation causes 33,000 extra cancer cases in the UK each year.

The first author, Isaac Allen, from the department of public health and primary care at the University of Cambridge, said: “This is the biggest study ever to examine second cancers after breast cancer and the first to show that women diagnosed with breast cancer in deprived regions are more likely to get second cancers. Many cancers are caused by deprivation, but more research is clearly needed to identify the specific factors driving the higher risks and how best to reduce these inequalities.”

In addition to data from more than 580,000 women, the authors examined the risk of second primary cancers for more than 3,500 male breast cancer survivors diagnosed between 1995 and 2019 using the national cancer registration dataset.

Male breast cancer survivors were 55 times more likely than the general male population to develop contralateral breast cancer, 58% more likely than the general male population to develop prostate cancer and had four times the risk of thyroid cancer, although the actual numbers of these cancers were low.

Responding to the findings, Prof Pat Price, a leading oncologist and co-founder of the Catch Up With Cancer campaign, said: “This highlights yet another instance of alarming inequalities within cancer, underscoring the urgent need for a dedicated cancer plan. Where one comes from or their socioeconomic status should not determine the chances of developing or surviving cancer.”

Dr Simon Vincent, the director of research, support and influencing at Breast Cancer Now, said while the higher risk of secondary cancer may occur due to genetic factors or the effects of initial breast cancer treatment, more research was needed into the causes of second primary cancers and how to follow up patients completing primary breast cancer treatment.