The drug is marketed under the name Erbitux
A decision to allow patients in Wales to get a "lifeline" bowel cancer drug - which add around five months to their lives - is likely to be overturned.
Health Minister Brian Gibbons approved the use of cetuximab in June, making Welsh patients the first in the UK to receive the drug.
But the UK's health watchdog said on Monday it would not recommend its use as it was not cost effective.
Oncologist Professor John Wagstaff said the decision was a "significant blow".
Cetuximab can delay the spread of advanced cancer and shrink tumours. It is prescribed to patients when all other forms of cancer therapy have failed.
In Wales, suitable patients can currently receive 18 weeks of treatment on the NHS, costing £600 a week.
But The National Institute for Health and Clinical Excellence (Nice) has published final recommendations which conclude the treatment is not "a good use of scarce NHS resources".
Deputy chief executive Andrea Sutcliffe said: "The evidence available on cetuximab does not compare it to current standard treatment and therefore we are not able to assess whether it is any better than existing treatments or whether the NHS could justify spending money on the drug."
BOWEL CANCER FACTS
Bowel cancer is the UK's second biggest cancer killer
35,000 are diagnosed every year - 95 a day
16,000 die from bowel cancer every year - 44 a day
30% of patients do not present themselves until the cancer has spread, making treatment more difficult
The five-year survival rate for patients with advanced bowel cancer is less than 5%
Final guidance on the use of the drug is expected in November.
The Welsh Assembly Government said if the recommendations by Nice were finalised, patients in Wales currently receiving the drug would continue to do so.
Prof Wagstaff, from the South West Wales Cancer Institute in Swansea, said the decision was a "significant blow" to patients and oncologists in Wales.
He said: "Cost should not be the deciding factor in how we treat our patients, especially when a drug has proven efficacy and is widely used in the rest of Europe."
Hilary Whittaker, chief executive of Beating Bowel Cancer said Nice's decision was "a scandal" which had left her members "extremely angry" as the drug was available across to people with advanced bowel cancer.
She said: "So the UK is the only country now that doesn't have it but it is particularly difficult in Wales because we're concerned about what it going to happen to patients who have already started treatments.
'Quality of life'
"It's absolutely unacceptable to make a decision based on cost alone. We think a lot more consideration should be given to the quality of life [of patients].
Hayley Sandrey, from Llanedeyrn, Cardiff, has suffered bowel cancer and said it was crucial that other sufferers had access to the treatment they need.
She said: "I think it's cruel to be able to say 'we've got something that could help you, we were going to give it to you but now we're not going to,' you can't do that to people.
"It's totally inhuman. I think it's just plain cruel to do that purely on the matter of cost."
Dr Tim Maughan, a Professor of Cancer Studies at Cardiff University College of Medicine, said Nice's recommendation was "understandable, if disappointing".
He said: "I think when we know who benefits the most and when to use it, it will become available again, but we need the results of those trials and they are ongoing at the moment."
Consultees can appeal against the recommendations, but the assembly government has said it was unlikely to do so.