As his condition continued to deteriorate, his family issued an emotional plea to the public for a new liver donation to save his life.

The heart and lungs from the same dead donor had already been transplanted into other patients when a 1.5cm tumour was found in the donor's kidney at Prince of Wales Hospital. The Sha Tin hospital apologised and explained the cancer was too difficult to detect.

A medical expert said a tumour of that size indicated a very early stage of cancer.

READ MORE: Hong Kong hit with second medical blunder in a week as organ donor posthumously found to have cancer

The University of Hong Kong's head of surgery, Professor Lo Chung-Mau, a world expert on liver transplants, yesterday defended his team's decision to shelve the liver operation. He said the patient's organ had not been dissected when the medical team was notified that cancer had been found in the donor's kidney.

"There is always a risk of passing cancer cells down from the donor to the recipients," Lo said. "The organ should no longer be used in transplantation if the organ donor was found with cancer, or else it would be a serious violation of medical ethics."

But a patients' rights group called for the guidelines in using donated organs to be reviewed, arguing it was important for patients to be able to make an informed choice in such cases.

"Patients' safety should come first. However, if the patient is too old to wait, or there is an urgent condition, the risk might be worth it for them," said Tim Pang Hung-cheong, spokesman for the Patients' Rights Association.

In contrast with local regulations, standards overseas are more relaxed in transplanting organs donated by cancer patients. A British guideline states that "organs from deceased donors with some current and past cancers may be safely used". It classifies the risks of using such organs on five levels, according to the stage of cancer.

The standard published by the British government's advisory committee on safety issues, said kidney tumours larger than 7cm, for example, were considered to be high-risk - there was a more than 10 per cent risk of transmitting the disease.

However, if the cancer was smaller than 1cm, the risk was minimal, with likelihood of transmission at less than 0.1 per cent.

The American Cancer Society states that "under certain circumstances" there may be an acceptable risk in using organs from donors who have had certain types of cancer, for instance a brain tumour that has not spread beyond the brain stem. Both guidelines stress that donations are not advised if the cancer cells are "actively spreading" or have spread outside an organ.

An associate professor of oncology at Chinese University, Stephen Chan Lam, said it was debatable whether organs from donors with cancer could be used in transplants. Doctors would have to gain the consent of recipients and their families.

He believed the doctors at Queen Mary Hospital had done their best in Lee's operation.

"Of course it was theoretically possible to seek consent from the patient and his family on whether they wanted to take the risk, but I believe it was practically difficult for doctors in this case as the operation was already under way," Chan said.

The doctor would normally assess the risk to recipients and allow them and their relatives time to ponder the possible complications and benefits before making a decision, he said.

A doctor who preferred not to be named said ceasing the operation was the safest option - for both patient and doctors - as medical staff could face a lawsuit if the recipient developed cancer at a later stage.

"Sticking to the guidelines is always the safest thing to do in a situation like this," the doctor said.