There is a charge of €75 a night for in-patient services in public hospitals, capped at €750.
Hospitals are also entitled to impose the €75 charge on day services but, until recently, most exempted cancer patients.
The Irish Cancer Society is concerned that cancer patients whose treatment phase spans two calendar years will have to pay €1,500.
About 30,000 people in Ireland are diagnosed with cancer every year and the number is expected to rise to over 40,000 per year by 2020.
The society’s spokeswoman, Kathleen O’Meara, said it is possible that a cancer patient could reach the €750 ceiling in one year as an in-patient and be charged again the next year for day services.
“Anybody who would be diagnosed with cancer in the middle of the year would certainly be in that situation,” she said.
Nursing services manager with the society Joan Kelly said most chemotherapy regimes would be at least six months and some would be up to one year.
Ms Kelly said a patient diagnosed with cancer sometime after the middle of a year would cross over into the next, where they could be charged €750 a second time if the hospital demanded it.
The charge does not apply to medical card holders and those with private medical insurance.
The society said many people undergoing standard treatment for cancer would not have a card or insurance. “A lot of people have given up private medical insurance but may be still over the income limit for the medical card,” said Ms O’Meara.
The medical card is means tested and is usually only given to cancer patients with an immediate need because of seriously ill health.
The HSE sometimes reduces or waives the charge in cases of hardship.
The society said some cancer patients waiting for medical cards were receiving letters from debt collection agencies demanding payment of the charges.
Ms O’Meara said the HSE’s use of debt collection agencies to chase the non-payment of bills could be having additional psycho-social effects on patients.
The society provides over €1m a year to cancer patients needing financial help — about 5% of its total annual spend and most of which is directed at patient services.
Ms O’Meara said applications to the charity’s financial aid scheme had increased by 36% in the last three years. She pointed out that 1,700 people applied for a payment under the scheme because they were struggling to cope financially.
Queries about cancer costs, such as heating and travel, are now the third most frequent type of call to the National Cancer Helpline (1800 200 700).
“If someone is self-employed, young, without private health insurance, not eligible for a medical card, or doesn’t have savings, they are left in a very vulnerable position of being unable to manage basic expenses, such as heating and travel to hospital for treatment,” said Ms O’Meara. “We are hearing from an increasing number of these people.”
The top three reasons for needing financial help are heating and fuel (50%), travel expenses (25%), and childcare (7%).
The Irish Cancer Society said the financial supports for patients were a last resort — it tried to help people explore the other options available to them.