Cancer services should continue to be a priority despite an expected squeeze on public spending, say cancer charities.
Wales Cancer Alliance representatives will call on the assembly government to ensure services are not jeopardised.
Public services in Wales are facing cuts that will cause "considerable pain", according to a recent report from the auditor general for Wales.
The assembly government said it regarded health, including cancer care, as an "essential public service".
Cath Lindley, chair of the alliance and general manager for Macmillan Cancer Support in Wales, said the "scale of the challenge" facing the assembly government to ensure everyone affected by cancer in Wales was offered the best treatment and support is "enormous".
"This is why we are taking the opportunity to call on government to ensure that cancer services are not neglected or put in jeopardy by the inevitable and very real spending squeeze facing our public services," she said.
The call, which will be made at the Wales Cancer Conference in Cardiff, comes as a new poll commissioned by Macmillan Cancer Support suggests 66% of people in Wales believe cancer ought to be one of the illnesses or diseases given the highest priority by the assembly government.
Gillian Body, the auditor general for Wales, has said the NHS, councils and the police may need to cut staff hours and encourage part-time working to deal with budget cuts.
She said services must work in "radically different ways" to face up to cuts of some £1.5bn.
Prof Ceri Phillips, a health economist at Swansea University, said cancer services had benefited from relatively generous funding in recent years.
"Cancer has been given a high priority in terms of health policy and expenditure, and quite right too," he said.
"If I was a patient with cancer I would want money spent on cancer, if I had some other condition my priorities might lie elsewhere.
"The choices to be made are pretty hard. We've been very generous to cancer over recent years.
"What we've got to ensure is that whatever the health budget is in Wales, we've got to get the most out of it."
The assembly government said in a statement: "With one-in-three people diagnosed with cancer at some stage in their lives, investment in caring for people with cancer and measures to reduce the incidence of cancer has, and will continue to be, a priority for the Welsh Assembly Government.
"The first minister has made clear on a number of occasions that funding levels for the next financial year are going to be extremely challenging.
"We regard health, and cancer care as part of that, as an essential public service."