The controversial decision by the National Institute for Health and Clinical Excellence not to approve two new bowel cancer drugs was due to quality of life issues, according to charity Cancerbackup.

When the health watchdog assesses new medicines, it looks at the cost per "quality-adjusted life year" (QALY) in relation to price, months or years of added survival, side-effects, and whether it improves quality of life.

But the net financial cost appears much smaller than assessed outlay, which can cause consternation among patient groups.

Hannah Saul, Cancerbackup's policy and public affairs manager, said pharmaceutical firms and the Department of Health needed to ensure new drugs met Nice's affordability threshold of £30,000.

She said: "Herceptin costs between £22,000 and £27,000 per patient on the NHS but it has a QALY of less than £5,000 because it's so effective - patients rarely develop advanced cancer - which adds years on to their lives and saves the NHS money.

"But because the two bowel cancer drugs - Avastin and Erbitux - have much higher QALYs, and the benefit is measured in months rather than years, Nice seem to have homed in on the cost.

"While they do make some really difficult decisions, and we understand where they're coming from, on this occasion we disagree with their decision.

"We've got to decide, as a society, how we're going to make this equation more balanced so it will give patients and doctors these extra options."

Avastin is currently being tested as part of other potential cancer treatments, and the results of these trials are expected next year. But unless it produces "Herceptin-style" outcomes these too could be rejected by Nice on cost grounds.