NHS cancer care in England is getting better according to a report by the National Audit Office.
But the NAO warns that a lack of reliable statistics is holding back further improvements.
It estimates that cancer care cost the NHS in England £6.3bn in 2008-09.
A lack of data means the Department of Health cannot say if its Cancer Reform Strategy, published in 2007, offers value for money, it adds. Ministers say a review is to take place.
Around 255,000 people a year are diagnosed with cancer, the vast majority of them over the age of 60.
With an ageing population that figure is expected to rise to around 300,000 by 2020.
Cancer is also the biggest cause of death in the under 60s.
The National Audit office report sees clear signs of improvement - even as more people are diagnosed with the disease, the death rate is falling.
The UK as a whole still lags behind the performance of other leading European Union countries and it was this that the Cancer Reform Strategy was set up to address.
The NAO report examines whether this strategy provides good value for money but it finds that a lack of reliable information means it is very hard to judge.
For example, data on chemotherapy treatment and outcomes is described as "poor" and the introduction of national figures on chemotherapy is two and a half years behind schedule.
There are also unexplained variations in the amount spent on cancer care by Primary Care Trusts.
So in 2008-09, one PCT spent £55 per head, while another spent nearly three times that amount, at £154 per head.
The NAO says it is impossible to tell whether this results in patients receiving better treatment or getting better outcomes.
But one area of improvement is a reduction in the number of hospital admissions for cancer patients.
Admitting someone to hospital is a very expensive way of treating their cancer when many people could be dealt with as day patients.
The NAO says that £113m a year could be saved if the average length of stay in hospital was reduced to the level of the best performing PCTs.
Improvements in the use of radiotherapy machines could also help the NHS meet increased demand.
The Department of Health says it is carrying out a review of the Cancer Reform Strategy this winter and the report will be used as part of that process.
The care services minister Paul Burstow said the aim is to get cancer survival rates up among the best in the world.