Cancer patients may be missing out on the most effective treatments because of poor access to new biomarker tests, according to a survey of senior hospital doctors.
Three-quarters of the 100 UK oncologists who took part in the online poll said they were having to overcome barriers to the use of targeted medicines.
More than half (53%) of the consultants and registrars admitted they "often or sometimes" prescribed a treatment that was not necessarily the best choice for an individual patient because of lack of access to tests.
And 22% said patients were sometimes given drugs without reference to test results that could indicate whether or not the treatment will work.
Cost and red tape within the NHS were cited as the main obstacles.
The tests are used to identify patients with particular genetic make-ups or blood proteins that make them suitable for specific therapies.
Lung, breast and bowel cancers and leukaemia are the key diseases where such "personalised medicines" have become available.
One of the first examples of a targeted drug requiring a biomarker test was the breast cancer treatment Herceptin. It is only effective for women with an over-active Her2 (human epidermal growth factor receptor 2) gene.
Another gene called KRAS appears to play a key role in bowel cancer. While 60% of patients have a version of the gene that means they may benefit from an antibody drug called cetuximab, the remaining 40% are not helped by the treatment.
The survey was sponsored by drug company Merck Serono which announced last year it would fully fund KRAS biomarker testing for all UK patients diagnosed with bowel cancer.
A background briefing report highlighting the findings is being sent to MPs and peers.
Dr Tim Iveson, consultant medical oncologist at Southampton General Hospital and a member of the charity Bowel Cancer UK's medical board, said: "These findings are extremely worrying. It is simply not acceptable that some patients are not getting the treatment that they deserve.
"In bowel cancer, we are making headway, with biomarker testing standardised and provided to every patient by the pharmaceutical industry. We need more collaborations like this between the NHS, the pharmaceutical industry and government to ensure better use of stretched NHS resources and to make sure that individual patients are receiving the very best treatment possible that will lead to the best outcomes and where possible, extend life."
A majority of the specialists surveyed agreed that access to biomarker tests for personalised medicines varied in different parts of the country. More than a fifth said they would be more likely to offer a personalised medicine to a private patient rather than an NHS patient.
A key factor influencing whether or not patients had the tests was cost.
Long delays in obtaining the results of tests from specialist laboratories were seen as another problem. Around half the oncologists said tests results took at least two weeks to arrive which was considered too long.
Health Minister Lord Howe said: "We have set out our commitment to halve the gap between the survival rates in England and the best in Europe by 2014/15 - and our long-term aspiration to be as good as the best.
"To deliver this, we must ensure not only that we tackle late diagnosis of cancer but also that all patients get the best possible treatment for their cancer.
"Using molecular testing of cancers to match individuals to the most appropriate treatment is a revolutionary way to help achieve this.
"We know that already around 30,000 of these tests are currently being undertaken in England, but we also know that we need to go further to make sure that all patients can benefit from them.
"That's why we are developing a new commissioning and funding structure which we expect to come into effect next year. We estimate that this will immediately benefit another 10,000 patients - but many more should benefit in the future."