Australian researchers have shown how a chemical similar to those used in cleaning products may benefit breast cancer patients.
Bisphosphonates, which resemble chemicals used as water softeners in soap powders and detergents, are currently used clinically to treat conditions that affect the bones.
The calcium-binding drugs are prescribed to people with osteoporosis and those with late-stage cancers that have spread to bone.
In recent years there have been a number of trials suggesting these drugs prolong survival in women with breast cancer.
However, researchers did not exactly know why.
In the medical world, it has been assumed bisphosphonates would not get into tumours other than bone cancers at any concentration that could make a difference.
Now a team from Sydney's has used imaging technology to show exactly how the drugs can target cells in tumours outside the skeleton, including breast cancer.
"This study is potentially transformative for treatment of some cancers, because it is telling us for the first time that drugs we thought acted only in bone can also act within tumours completely outside the skeleton," says project leader Professor Mike Rogers.
Breast tumours often contain particles of calcium.
Calcium phosphate - the predominant form of calcium seen in breast tissue - is frequently associated with malignancy.
To see if bisphosphonates interact with breast calcium, the researchers attached to a chemical that glows under a microscope to the drug.
They then gave the medication to mice with breast cancer and watched on a screen what happened.
"For the first time we're able to see in a live animal exactly where the drug was going," said Prof Rogers.
The imaging videos show how the bisphosphonates attach to tiny calcifications in tumours. The calcium and drug complexes are then devoured by tumour-associated macrophages - immune cells that the cancer hijacks early in its development to conceal its existence.
After the macrophages have gobbled up these complexes they then switch sides and attack the cancer.
"We do not yet fully understand how the macrophages revert from being bad cops to being good cops, although it is clear that this immune cell interacts with tumours, and probably changes its function in the presence of bisphosphonates," said Prof Rogers.
Once the team realised what was happening in mice, they obtained a tumour sample from a patient with breast cancer who had undergone surgery.
Tests on the tissue indicated the same process happens in humans.
The study is published in the journal