There may be fresh hope for prostate cancer patients who develop resistance to traditional forms of therapies, as oncologists say a new third-line treatment is showing promising results so far.

The Hong Kong Society of Uro-Oncology said the targeted radiotherapy treatment -- lutetium-177-PSMA-617 -- can boost cancer survival rates and improve patients' quality of life.

Half of the patients also reported a reduction in tumour size, while others had cancer cells completely eradicated.

The treatment is used when the patient no longer reacts to both hormonal therapy and chemotherapy, and presents symptoms such as difficulty in urinating, blood in urine, and even spinal cord pain.

Clinical oncologist Kenneth Wong said the treatment is also associated with less side effects.

"There are certainly some side effects associated with the use of this drug, including dry mouth, fatigue, nausea, anaemia and so on," he said.

But that was still better than traditional chemotherapy, Wong stressed, in which patients had to deal with suppressed bone marrow function and an increased risk of infection.

The theranostic medicine is administered intravenously every six weeks, for up to six sessions. It locates cancer cells in the body and delivers targeted radiation to kill those cells.

Wong said patients are required to drink large amounts of water to purge the remnants of the drug which are not absorbed by the tumour.

They should also avoid close contact with people for up to two weeks, especially children and pregnant women.

Each injection costs HK$150,000 and public hospital patients have to pay out of their own pockets. Charity group St James' Settlement currently provides a subsidy of up to HK$30,000 for each treatment programme.

Prostate cancer was the third most common cancer among men in Hong Kong in 2021. More than half of the patients were only diagnosed at an advanced stage.