Primary care trusts could come under pressure to refund tens of thousands of pounds to patients who have paid for top-up treatment.
One PCT has already refunded more than£23,000 to two patients who paid for care that was later deemed to be the responsibility of the NHS.
Another faces a demand for nearly£60,000 from a patient who initially funded his own treatment with Cetuximab before being accepted by the NHS as an exceptional case. The patient's lawyer told HSJ that if the PCT did not pay up, their fight would go to court, where they hoped to set case law.
PCT network director David Stout warned that in the absence of clear guidance on how to handle retrospective claims, PCTs were likely to come under pressure to follow precedents set by others.
Worcestershire PCT agreed to "compensate" two patients for the cost of NHS care they were forced to pay for while receiving Avastin for bowel cancer. Barbara Moss was awarded£13,658 of her£21,000 treatment bill and Clifford Shore got£10,000 of his£16,000 costs.
A PCT spokeswoman said the PCT had taken legal advice. "We don't believe this will set a precedent across the country; it will be up to individual PCTs to look at cases individually, as we did," she said.
Patient Michael Porter is challenging East and North Hertfordshire PCT to refund£55,900 that he used to pay for Cetuximab. His claim rests on the fact he responded well to the drug and was subsequently accepted as an exceptional case by the PCT.
Swaffields Solicitors principal Simon Swaffield, representing Mr Porter, said: "It's not satisfactory from a health service point of view to just muddle along and if you make enough noise, you might get some money.
"The reality is we've taken Michael's case forward on this footing, very much with a mind to establish liability."
Mr Stout said PCTs were expected to make judgements on whether to reimburse or not "without any real framework within which to work".
"If some PCTs start [reimbursing], I'm sure that ratchets up the pressure on other PCTs to do the same," he said.
He also said that where a patient had secured exceptional case funding on the basis they had proved a drug's efficacy by self-funding initial courses of treatment, this breached the principles of the Richards review of co-payments because it created inequity.
A Department of Health spokesman said it was up to PCTs to determine whether to issue reimbursements or not "in light of the individual circumstances of each case".
He added that responsibility for exceptional case decisions remained with PCT exceptional case committees.