An INJECTION to reverse the effects of the genes which cause breast cancer could help women avoid invasive therapies, researchers believe.Currently, women with early signs of breast cancer or those carrying genes linked to the disease face difficult decisions about different treatments or mastectomies.But new research from Harvard University in the United States suggests that women could be given treatments which block the effects of the genes, removing the need for surgery, chemotherapy or radiotherapy.Campaigners in the UK welcomed the findings.Current treatments work by killing cancer cells, but can often also damage healthy tissue and lead to severe side-effects.However, researchers at Harvard'sWyss Institute in Boston thought they could create better therapies by spotting the genes that cause breast cancer and blocking them before they start to drive the development of tumours.Identifying these genes is difficult because many thousands are active in cells at any one time. This can lead to some being wrongly labelled as causing cancer.To get round this problem, the researchers used a sophisticated mathematical model to "reverse-engineer" the complex gene networks in cancer cells.This method helped the scientists find more than 100 genes acting suspiciously just before milk-duct cells in the breast began to overgrow, signalling the start of cancer.They then narrowed down the list to six genes with the ability to turn other genes "on" or "off" - making them active or inactive. These were finally refined to just one gene, known as HOXA1, which had the strongest statistical link to cancer.The scientists went on to test whether they could reverse cancer in mouse cells in the lab by blocking HOXA1 using "small interfering RNA" - molecules involved in how genes behave in the body.The study found that the treatment successfully stopped the development of cancer and helped healthy tissue to grow.It also stopped the disease in mice genetically engineered to have a gene which causes cancer. Nanoparticles were used to inject the treatment directly into the milk ducts of the cancer-prone mice. After several weeks, the treated mice were found to be healthy, while untreated mice developed breast cancer.Researcher Amy Brock said: "There was no 'Aha' moment, but after enough evidence builds up, you turn to each other and say, 'This is really doing something here'."It is hoped the findings, published in the journal Science Translational Medicine, could help women who carry genes which entail a high chance of developing breast cancer, such as actress Angelina Jolie who last year had both her breasts removed to help prevent the disease.Dr Emma Smith, Cancer Research UK's senior science information officer, said: "This research is a promising step forward. But there are many different types of breast cancer and there is no evidence yet that this approach will be safe or effective for women, or what the long-term side-effects may be."