Cancer patients and their families are 20 times more likely to ask for help about financial issues than death and dying, figures suggest.
Four out of 10 callers to Macmillan Cancer Support's helpline in 2011 asked for help on financial issues, including accessing benefits, compared to just under 2% who sought information and support on death and dying.
Overall, calls to the helpline on any topic rose by around 30% to 122,000 in 2011 compared to 2010.
According to the charity, financial difficulties are set to get even worse for cancer patients and their loved ones, with Government changes to welfare meaning around 7,000 cancer patients will lose up to £94 a week each.
Mike Hobday, director of policy and research at Macmillan Cancer Support, said: "During the biggest fight of their lives it is shocking that more and more cancer patients have to spend time seeking help about financial issues rather than focusing on their health and wellbeing.
"While we recognise the benefits system is in need of reform, if the Welfare Reform Bill goes through unamended it will have a devastating effect on cancer patients who are already struggling.
"We know many Lords oppose these proposals and hope they will show their support for cancer patients when it comes to a vote in Parliament."
A spokesman for the Department for Work and Pensions said: "Our proposals would give cancer patients the choice to get financial support for as long as they require it whilst leaving open the option to work.
"Everyone agrees that for some people being able to continue working or getting back into work after diagnosis is important and we want the support we give to reflect that."