When samples of breast tissue show the presence of a malignant tumor, doctors often prescribe surgery followed by a six-month treatment of medicine, which can include chemotherapy to prevent further spread of cancer cells.

Chemotherapy kills the remaining cancer cells but also has adverse side effects – nausea, hair loss, fatigue, as well as possible infertility and damage to some organs.

“We know that some drugs can affect the heart. There's a question about long-term effects of slightly increasing the risks of dementia for instance. Apart from that, of course, there's the unpleasantness of the four months of treatment that's required, and it'll often take people out of work for six months," said Dr. Simon Holt, of the Prince Phillip Hospital in Wales.

A new test developed in the U.S., called Oncotype DX, determines how the patient will respond to chemotherapy.

“Oncotype DX is effectively telling you about the inside workings of the cell, which particular genes have gone wrong to create that particular cancer, and, from a reading of those genes, we can then get more information about whether this tumor is the sort that is likely to spread to some other part of the body, or not,"  Holt said.

Avoiding chemotherapy after surgery means that patients like Nia Barton can resume their normal lives except for regular checkups to make sure they remain cancer free.

Oncotype DX is one of several gene-based tests that can tell doctors how likely the recurrence of the disease is, and it is most accurate in the early stages. Similar tests, such as Prosigna and Endopredict, are undergoing clinical trials in the UK, Germany and Austria.

So far, Oncotype DX is used only in cases of breast cancer, but researchers say similar tests can be developed for other types of cancer.