The demand of the charity is that parking costs be made free or subsidized.
"These regional variations are shocking and grossly unfair - cancer patients in Scotland and the South West can pay almost double the costs. Missing an appointment is not an option for cancer patients - they have no choice but to pay for travel and parking, which amounts to a stealth tax on illness," said Macmillan chief executive Peter Cardy.
The assistance should come from the hospital travel costs scheme. It pointed out that due to the nature of cancer, patients make an average of 53 trips to hospital.
Gill Morgan, chief executive of the NHS Confederation said, "It is not as straightforward as it seems to abolish all car parking charges. Some NHS hospitals have a very limited supply of car parking and are unable to provide free parking for all patients, which is why charges are used as a way of managing demand."