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In an important step forward for personalising care for women with breast cancer, researchers have found that a molecular test can pinpoint which patients will have a very low risk of death from breast cancer even 20 years after diagnosis and tumour removal.
As a result, 'ultralow' risk patients could be treated less aggressively and overtreatment avoided, leading to fewer toxic effects.
"We can now test small node-negative breast cancers, and if they are in the ultralow risk category, we can tell women that they are highly unlikely to die of their cancers and do not need aggressive treatment, including radiation after lumpectomy," said lead author Laura Esserman, breast cancer specialist and surgeon with University of California Health System, or UC Health.
Oncologists have discussed the existence of ultralow risk tumours and expressed concern that they might be exacerbated by screening.
But this study, published in the journal JAMA Oncology, provides the first evidence that it is possible to run a test at the time of diagnosis and identify them, according to Esserman.
"This is an exciting advance because approximately 20-25 per cent of tumours diagnosed today may be ultralow risk," said Esserman, who is also a professor at University of California, San Francisco (UCSF).
The medical community for many years has focused on identifying cancer early so that it can be cured or more easily treated.
While this can benefit some patients, screening also can detect cancers that are extremely low risk and not life-threatening, which could lead to patients being overtreated.
The issue is compounded because breast cancer can recur many years after diagnosis -- for low-grade tumours, the majority of the risk occurs after five years.
Until now, tools that could reliably identify ultralow risk tumours at the time of diagnosis have not been available because physicians lacked the assurance that late recurrence could truly be avoided.
In the new study, researchers sought to determine whether a 70-gene test could accurately and reliably identify tumours with indolent, or slow-growing, behaviour to assess the risk of cancer recurrence up to 20 years after diagnosis.
The test, called MammaPrint, was devised by UCSF cancer researcher Laura van't Veer, a co-author of the new study that involved 1,780 patients.
The results suggest that the 70-gene test can be used to help physicians and patients determine their treatment course, and to inform choice of systemic therapy as well as local therapy.
"There are breast cancers that pose little or no systemic risk," said Esserman.
"Women who have a tumour that is classified as ultralow risk by 70-gene signature can be reassured that their long-term outcome is expected to be excellent," Esserman added.