The Irish Cancer Society says cancer patients are spending an average extra cost of €756 per month, rising to over €1,000 in some cases.
It says these costs relate to medical expenses that cannot be claimed back - costs associated with appointments, increased day to day living expenses and many other expenses - that they did not have before they were diagnosed with cancer.
The society released their second 'Real Cost of Cancer' report, which finds that cancer patients are also losing an average of €18,000 a year in income, or over €1,500 per month, as a result of their cancer diagnosis.
It finds that the average costs associated with visiting hospital for appointments or treatment - such as petrol, parking and eating in the hospital - was €291 per month.
The average cost of medicines and medical expenses was just over €261 per month, while one in 10 had costs from hospital stays - the average was €288 a month.
And GP charges were an additional €81 per month.
It also says one in three people change their employment status and one in four changed their approach to work.
CEO of the Irish Cancer Society is Averil Power: "Cancer is crippling people financially. Patients in Ireland devastated by a cancer diagnosis are then going on to really struggle to make ends meet.
"At a time where they should be focusing on their health and getting through their cancer treatment, they are worrying about bills stacking up.
"Most patients and often their partners are already suffering huge losses in income.
"This can result in people having to choose between paying hospital charges over putting the heating on. It could also mean choosing to buy medication over putting food on the table. Nobody should have to make that choice."
Sinead Kealy from Donabate in Dublin was diagnosed with non-Hodgkins lymphoma months after giving birth to her first child.
She says: "It took my family 10 years to recover from my cancer diagnosis.
"I lost over €18,000 in earnings while I was in treatment and built up a credit card debt of €12,000 - all as a result of my cancer.
"It was like being hit by a bus. It changed my life completely."
"Besides thinking about how or if I would survive this diagnosis, things like heating costs, childcare, parking and food were a constant worry.
"It was daily struggle to get by and I often had to turn to the credit card.
"I live in fear of my cancer returning because I honestly don't know how I would cope again financially."
Ms Power adds: "We are calling for action so that no one is more worried about bills mounting up than they are about getting better.
"We need the Government to stop the endless charges it levies on cancer patients.
"We need better access to medical cards and a greater appreciation of the huge financial strain of having cancer.
"The double whammy of increased costs and loss of income needs to be taken into account when considering what cancer patients can reasonably bear."
Anyone concerned about cancer can contact the Irish Cancer Society Nurseline on 1800-200-700
Main image: Chief executive of the Irish Cancer Society, Averil Power | Image: Leah Farrell/RollingNews.ie