The malfunction occurred at a satellite pharmacy for the Western General Hospital in Edinburgh, which is home to the capital's cancer centre where patients from throughout the south east of Scotland are treated.
Chemists were alerted overnight by an automatic alarm, which is set off if there is a deviation from the fridge's set temperature. It is believed the valuable stock was stored at four degrees less than its recommended level for up to two hours.
In an attempt to save the drugs, staff contacted the manufacturer to find out whether they had information on the impact the temperature drop would have on their effectiveness. However, as no studies had been carried out, NHS Lothian staff took the decision to destroy the contents of the fridge.
Dr Jean Turner, director of the Scotland Patients Association and a former independent MSP, blamed a management failure and said taxpayers' money had been thrown down the drain as a result.
"Since drugs are so expensive I would have thought the fridge is something that they would have been checking on a daily basis," she said. "This is sad because so many cancer patients struggle to get the medication they need because of how much it costs.
"In a hospital like that, you need to be on the ball from a maintenance perspective. It's sheer waste."
The value of the stock was so great that the health board, which has said it expects to have to make savings of £400m over the next decade, was forced to seek retrospective approval from the Scottish Government to write off the loss.
Scottish Conservative health spokesman Jackson Carlaw said: "This has turned out to be an expensive mistake for NHS Lothian. It's important lessons are learned from this incident to ensure it doesn't happen again in the Lothians or anywhere else.
"And while the loss of tens of thousands of pounds worth of drugs is far from ideal, we have to realise that in an organisation the size of the NHS this kind of thing will always happen.
"The priority is to make sure no patient loses out as a result."
While no patients went without the necessary medicines as a result of the malfunction, an investigation was launched into how it occurred.
The cause is believed to be an "age-related failure" of the six-year-old fridge's temperature controller.
Following the incident, which occurred in February and has only recently been made public after the minutes of a behind-closed-doors meeting were published, it was decided new temperature controllers would be ordered for the other fridges in the pharmacy that were of a similar age. In future, they are to be replaced every two years.
However, members of the health board's audit and risk committee said it was not satisfied that enough had been done to avoid a repeat, and requested a more in-depth investigation from NHS bosses.
Professor Angela Timoney, NHS Lothian's Director of Pharmacy, said: "As soon as we were notified of the fridge failure, appropriate action was taken and there was no impact on patient care.
"We have taken significant steps to prevent this type of failure occurring again, including replacing the temperature controllers and installing secondary fail safe controllers."