Researchers develop new test for early diagnosis of nasopharyngeal cancer
Hong Kong and Canadian researchers have developed a simple test that enables early detection of nasopharyngeal cancer – popularly known as Guangdong cancer because of its prevalence in southern China – that is usually discovered only in its late stages.
They expect the viral genetic test to be helpful in screening patients with family history of the disease as well as checking for recurrence in treated patients.
“It is a very accurate way to find nasopharyngeal cancer,” said Dr Raymond Ng Hin-wai, assistant professor in otolaryngology – or the study of ear, nose and throat conditions – at the University of Toronto.
“It is very simple and can be done in even remote regions reached by few specialists,” said Ng, who led the study on the test.
Samples are taken by sticking a special brush through the mouth to reach the pharynx, the area of throat behind the nose where the cancer, which is also strongly hereditary, develops.
It collects cells to check for the presence of the Epstein-Barr virus, a common member of the herpes family found in high concentrations in almost all sufferers from the cancer.
Ng said the traditional method, which sometimes required anaesthesia, needed skilled specialists and might cause slight injury. But the brush test was simple enough for use by family doctors and nurses in primary care clinics, he said.
Doctors from the University of Hong Kong, Queen Elizabeth Hospital and the University of Toronto spent 10 years developing the test. They designed the brush and a solution applied to it to keep the DNA collected fresh.
In the next step, the team will recruit about 100 high-risk people from Hong Kong, Singapore and Canada for a clinical trial on the test’s use in early detection.
“When you brush, you don’t have to rush the test back. The DNA is stable for up to 30 days in the solution without refrigeration,” University of Toronto surgery professor Patrick Gullane said.
Using the polymerase chain reaction technique – in which a single DNA sample can produce millions of copies – even a small amount of viral DNA in the early stages of cancer is detectable.
With the brushing method, as few as 5,000 cancer cells can be detected, compared to 100 million for an endoscopy sample.
The test has been used in some private hospitals and clinics in Hong Kong over the past six months, but has yet to be adopted in public hospitals. It is also being used in Canada and the United States.
The team conducted a 10-year clinical trial on 578 Chinese people in Hong Kong and Toronto who underwent both the traditional diagnosis tests and the brush test.
The researchers found the brush test had 99 per cent sensitivity and specificity – medical terms for measuring accuracy in ruling in or ruling out a disease.
Professor Dora Kwong Lai-wan, head of clinical oncology at HKU, said it was usually difficult to collect samples from patients after treatment to check for recurrence as tissues had been damaged by radiotherapy. Further studies would be done to see if the brush test could overcome this obstacle.