Fatal cases of breast cancer could be prevented if a bill to repurpose existing drugs wins government support, Breast Cancer Campaign has said.
It is thought multiple sclerosis, Parkinson's and Alzheimer's disease patients could also benefit.
The charity called on the government to seek licences for drugs that are no longer patented.
Using old drugs in this way could cost as little as 6p a day so treatment could be routinely available, it said.
'Seize the opportunity'
Breast Cancer Campaign was joined by doctors and other charities, such as the Alzheimer's Society and the Association of Medical Research Charities, in calling for the government to consider the move through a bill to change the law.
The bill will be presented to Parliament for a second reading on 7 November.
The charity said there was no incentive for pharmaceutical companies to seek a new licence for repurposing a drug, once a patent for the drug had expired, as they no longer had a monopoly on providing it.
There was no organisation responsible for seeking a licence, said Breast Cancer Campaign, which called for the government to take action to seek licences for such drugs.
It pointed towards evidence that old drugs repurposed in this way could be clinically effective.
Clare Keeling, at the MS Society, said simvastatin was a drug originally licensed for treating high cholesterol, but in recent clinical trails it had been shown to be effective in treating the disease.
"If successful, simvastatin for MS would address a significant unmet need as there is currently no treatment that can slow or stop the deterioration seen in progressive MS," she added.
Conservative MP Jonathan Evans, leading the bill, said: "I still hope that the government will seize the opportunity to commit to taking the straightforward step of supporting this important bill.
Evidence from MS
"This is a real chance to significantly improve access to low-cost treatments, some of which would bring a step change in improving mortality rates."
He said the bill would save many lives and urged the government to "show the clear support needed" for it to become law.
The MS Society said it "fully supports" the bill.
Mia Rosenblatt, at Breast Cancer Campaign, said it was "incomprehensible" the government was not supporting the bill and asked why existing drugs were not given the same priority and focus as new drugs when they "cost next to nothing".
A Department of Health spokesperson said: "Doctors can already prescribe drugs without needing to wait for a new licence, if they believe it is right for their patients.
"Licensing is not the real problem here: we need to look at other ways to support appropriate off label prescribing of drugs.
"The government will set out its full position on this Bill at its Second Reading on Friday 7th November."