Dr Brian Keighley, chairman of the British Medical Association Scotland, said in some cases tens of thousands of pounds were spent on drugs to extend cancer patients' lives for relatively short periods.
Speaking ahead of his organisation's annual meeting, the GP said the country had to debate the merits of these kinds of aggressive treatments and the effects they had on the NHS budget. But he stressed any decision had to be made at a society level, rather than being left to doctors.
Patient groups are concerned that many cancer treatments are being rationed by the NHS because they are deemed too expensive.
While the NHS budget for Scotland rose slightly this year, the increasing cost of energy, food and drugs has meant health boards are having to make efficiency savings just to stand still. In many cases this has included recruitment freezes and a reduction in the NHS workforce of more than 3,000 in the past year.
Keighley said the Scottish Government was facing a "budgetary cliff edge" amid concerns about the negative effect of cuts. But he said there were areas where wider debate was needed to decide if Scotland could still afford to pay for services where good outcomes were limited.
This included life-extending treatments provided to people at the end of their lives with illnesses such as cancer.
He said: "We have to make a decision on some of the oncological (cancer] treatments that have limited outcomes, remembering that 80 per cent of money is spent in the last three years of life. They must be looked at critically.
"We have to keep development and innovation and keep pressing the boundaries against the ravages of terminal illness.
"But at the same time we have to have some evidence base as to how appropriate it is to spend many thousands of pounds to prolong life for a matter of weeks or months.
"That is a decision not for doctors, but a decision for society."
Keighley said the benefits of expensive treatments needed to be seen in good outcomes for the patients receiving them. But he said people's views on the issue would depend on circumstances.
He said: "There are some treatments that cost many tens of thousands of pounds and if that is to be sustained then clear benefit in terms of not just longevity but useful longevity and quality of life must be the outcome.
"I do appreciate that one's perspective on the necessity for life-extending drugs depends on where you sit. If it was my mother I would fight for anything that could help her.
"I would emphasise it is not the all-seeing, prescient god-like doctor's decision. This is a decision for society because society has to realise that every 30,000 you spend on one course of treatment has a consequent effect on the number of cataract and other operations you can perform."
Another area which could be discussed, he said, was the provision of treatments thought to be less effective, such as varicose-vein surgery and ear grommets, used to ventilate the inner ear.
And he said the public may also have to accept some NHS services needed to be centralised, rather than being provided locally, to make them as safe and effective as possible.
In Scotland, the Scottish Medicines Consortium (SMC) already rules on the cost effectiveness of new drugs using a measure known as quality adjusted life years (QALYs) – assessing the cost of a treatment against the benefit in terms of patient survival.
The limit is currently set at around a maximum of 30,000 per QALY, but the SMC can recommend more expensive treatments in cases where there is something exceptional about a drug.
Andrew Walker, health economist at Glasgow University and adviser to the SMC, said: "Being QALY-based in our decision-making means you take into account someone's remaining life expectancy and how much good you are going to do for them.
"We would say that any price we pay for the medicine has to be in proportion to that to give us the appropriate cost per QALY."
Walker said in some cases the price of drugs was inflated by companies who believed they could command high prices because they were dealing with cancer. He said: "A lot of manufacturers appear to believe if you have got something like cancer on the label then you can double the price.
"We don't accept that premise."
Vicky Crichton, Cancer Research UK's public affairs manager for Scotland, said: "We know these drugs can be expensive. Government plans to move towards a 'value based pricing' scheme should help ensure the NHS is getting value for money from the treatments it is buying.
"This scheme needs to be flexible enough to include all the things that are important to cancer patients, such as extra time at the end of life, and improvements to quality of life."
A spokesman for charity, the Rarer Cancers Foundation, admitted there may be a case for not funding drugs which only extend life for a few weeks.
He added: "But what we are talking about is treatments which are able to extend life for several months, as well as alleviate symptoms. That amount of time can make all the difference in terms for cancer patients spending time with their family and sorting out their affairs.
"We would agree that the NHS needs to save money where necessary in its drugs budget, and efficiencies can be made. Although cancer drugs have a high unit cost, the length of time treatment is required is relatively low and the patients numbers are small, so the impact on the overall NHS budget is modest."
A Scottish Government spokeswoman said: "It is the role of the SMC to provide advice to NHS boards on the clinical and cost-effectiveness of newly licensed, prescription only branded medicines. Additional factors, such as whether a medicine substantially increases life expectancy and/or quality of life, will also be considered. These arrangements focus on patients having access to effective medicines to treat all conditions in accordance with clinical need."
Analysis: Dr Sarah Christie
THERE are no easy answers when it comes to making decisions on the provision of expensive life-extending treatments.
Dr Brian Keighley argues that this is not a decision for doctors but a decision for society. He is right: doctors make clinical judgments on the appropriate treatment for a patient within a range of treatments that are available on the NHS. They cannot be asked to make wider, social decisions about the relative cost of treatment and whether that cost is sustainable.
It is for society to decide whether all potential treatments should be on offer, even if the extent of the benefit to the patient is very limited, or whether that list of available treatments has to be restricted to those cases where the potential benefit to the patient is clear.
Obviously we would like to offer all treatments that have some kind of a benefit to a patient. But it is not always that straightforward. To put it bluntly, there is always going to be a cost-benefit analysis. It could be argued that patients should receive treatment even if it only holds out a glimmer of hope for them, but this comes at the expense of being able to provide other treatment services where the prospects of benefit to the patients is much higher.
One of the things that makes this issue difficult is the compelling nature of the arguments on both sides.
Everyone knows that the NHS works to a budget and that the budget is limited, but changing demographics and public sector cuts have brought these issues to the fore in a very real way. It will inevitably have an impact on patients because the reality of the financial constraints on the NHS means that questions have to be asked about the continued provision of expensive treatments that are of very limited real benefit to the patients who receive them.
These questions are questions for us all. We cannot expect doctors to answer them for us.
• Dr Christie is a reader in law and medical ethics expert at Robert Gordon University, Aberdeen