Many breast cancer patients have experienced cash difficulties after being forced to pay prescription fees, a survey says.
Cancer patients are not exempt from paying for prescriptions
The Breast Cancer Care poll of 164 women in England and Scotland found 42% had experienced financial problems and 15% had not taken drugs owing to cost.
The charity said ministers must review the charging system as some patients paid for hormone therapies for years.
But the government said it preferred to subsidise those on low incomes.
Under exemptions drawn up in 1968, people with certain conditions, such as diabetes and epilepsy, get free prescriptions, but they do not cover cancer patients once they are not being treated in hospital.
But Breast Cancer Care have pointed out that some patients have to take courses of hormone therapy for years to stop the disease spreading or coming back.
A 10-year course can cost £1,000. Patients are also charged for wigs and painkillers.
Christine Fogg, Breast Cancer Care's chief executive, said: "Thankfully more people with cancer are now surviving than ever before, but many are now being treated long-term which comes at a price.
"Prescription charges, on top of all the added costs that can come with cancer such as child-care and hospital travel, can place enormous strain on individuals and families.
"It is time for change. The government must commit to an urgent review of the current list of exemptions.
"No one should ever be forced to pay prescription charges for what may be life-saving treatment."
The warning comes as Wales prepares to scrap the charges next year. Similar proposals are also being examined by the Scottish Executive.
Peter Cardy, chief executive of Macmillan Cancer Relief, said: "Raising revenue by forcing cancer patients to pay for life-saving prescriptions is morally wrong - it is shameful that the sickest and most vulnerable people have to pay the most.
"Prescription charges amount to an unfair tax on illness. We believe the system is outdated and in need of urgent review."
But a Department of Health spokeswoman said people on low incomes, children, pregnant women and the over 60s all got free prescriptions.
"In England our policy is to use the finite resources of the NHS to give priority to helping people who may have difficulty in paying charges, rather than extending the exemption arrangements."
And she added more than 87% of all NHS prescription items were dispensed free of charge, but charges still provided a valuable contribution to NHS funds.