By looking at several genes in the tumour, the test – called Oncotype Dx – can assess how aggressive the disease is. This information can then be used by clinicians to help decide whether hormonal-based therapy is enough to treat the tumour or if chemotherapy is needed.
Initial data from the TAILORx trial being carried out by the US National Institutes of Health, and involving over 10,000 women with early-stage breast cancer, demonstrated that women given a low recurrence score by the test may effectively use hormone therapy alone. Patients with a recurrence score of 10 or less and receiving hormone therapy alone had a less than one percent chance of their cancer returning at five years.
'These findings will give women with early-stage breast cancer greater certainty that anti-oestrogen [hormonal] therapy will decrease their risk of recurrence and increase their chance for survival whereas chemotherapy will not,' says Dr Mary Lou Smith, a breast cancer survivor who helped design the study through her role as a leader in the ECOG-ACRIN Cancer Research Advocates Committee.
The Oncotype Dx test looks at the expression of 21 genes in the tumour. This information is used to calculate a recurrence score on a scale of 0–100 that predicts how likely it is that the breast cancer will recur; the lower the score the less aggressive the tumour is.
Although the test initially came onto the market in 2004 after being tested in archived breast-cancer tissue samples, until now the test's capability to predict whether a patient would or would not benefit from chemotherapy had not been fully evaluated in a clinical trial.
The patients involved in the study had early-stage breast cancer, small tumours that had no mutation in the HER2 gene, and no spread of cancer to their lymph nodes. The current guidelines in the USA recommend that these women receive chemotherapy to prevent the cancer from recurring, depending on the size or grade of the tumour.
In the trial, over 1600 women with a recurrence score of 0–10 (those at low risk of their disease returning) were randomly assigned to receive hormonal therapy without chemotherapy. At five years, 98 percent were alive, and almost 94 percent remained disease free, showing that some women can be effectively treated with hormonal-based anti-cancer drugs alone.
This means that patients who might benefit from potentially life-saving chemotherapy can be identified, while those who do not need it can be spared from unnecessary treatment and the side effects that come with chemotherapy.
'What we've shown is that if you have a low recurrence score, you do really, really well with [hormone] therapy alone,' says Professor Joseph Sparano, lead author of the study and associate chairman of oncology at Montefiore Medical Center.
'The likelihood of responding to chemotherapy would be nil. So I think we can be much more confident in making the recommendation to just use [hormone] therapy alone, especially in patients where we might have been a little skittish about recommending sparing chemotherapy.'
However, the score cut off-of 10 is only arbitrary, and it is possible that women with a higher recurrence score could also avoid chemotherapy. This theory is being tested as the trial continues to monitor patients with recurrence scores between 11 and 25, a group that represents a much higher proportion of patients.