Nicknamed Cantonese cancer, NPC affects the nasopharynx: that's the part of the head behind the nose, and above and behind the mouth. It's the most common cancer of the head and neck in Hong Kong. According to the Hong Kong Cancer Registry, in 2008, the last year for which figures are available, it was the fifth most common cancer among men in Hong Kong, and 12th among women. (It's roughly twice as common in men, and prognosis for males is also worse.) Although it mainly affects people from Guangdong, Guangxi and Hainan, it accounts for 18 per cent of all cancer cases in China. It also affects younger adults more than most other cancers, striking most commonly in their 30s and 40s.

There is at least some good news where NPC is concerned: its incidence in Hong Kong has been gradually falling over the past three decades, from more than 30 cases per 100,000 population to fewer than 10. No one's quite sure why. The problem is, NPC remains fiendishly hard to detect because most of its symptoms can easily be mistaken for those of far more benign conditions.

These include inflammation of the middle ear, potentially causing ear blockage; hearing loss and tinnitus, but only on one side; fever; nasal obstruction; nosebleeds; and headaches. 'People think there's nothing wrong, and 99 per cent of the time they're right,' says Dr Peter Teo Man-lung, an oncologist at the Central Comprehensive Cancer Centre. 'But the 1 per cent really matters.'

As in To's case, the symptom that often prompts sufferers to first seek medical attention is persistent lymph node enlargement, because it's less easily dismissed as something trivial. But this often manifests itself relatively late - and late diagnosis is the bane of NPC treatment.

'The distribution of the disease on presentation is still the same as it was 30 years ago,' Teo says. 'Stage three is still the most common stage of detection. It's important that we see more people present in stage one, but we're not seeing that yet.'

Dr Daniel Chua Tsin-tien, associate director of the Comprehensive Oncology Centre at Hong Kong Sanatorium and Hospital, says NPC does at least 'provide some hints for us to detect it in the early stages', hearing loss being key among them. But he agrees that early detection is still a problem: only 10 per cent of patients present at stage one, when prognosis is good, with a recovery rate of 90 per cent, he says. A further 30 per cent present at stage two, when their chances of recovery drop only slightly to 85 per cent. The most common stage to present is three - 35 per cent of patients - when the recovery rate is 70 per cent; and 25 per cent present at stage four, when it falls to 55 per cent.

Precisely what causes a person to develop NPC is unknown, but medical consensus points to three factors. 'Number one is racial,' Teo says. 'Certain southern Chinese are predisposed to developing NPC; several genes have been identified, the presence of which will predispose people to it.' So if a close relative has had the disease, it makes sense to get screened for it.

The second is infection by the ubiquitous Epstein-Barr virus, a member of the herpes family, which infects most people at some point in their lives and is associated with various cancers, Teo says.

The third is environmental factors, mainly diet.

'It's multifactorial, like lots of other cancers,' says Dr Ambrose Ho Chung-wai, associate ear, nose and throat (ENT) consultant, at Tung Wah Hospital. 'People don't know how the three factors interact with one another, but the genetic factor is the biggest. If people from Guangdong migrate, for example to the United States, the first generation get it at the same level, but the second generation don't. That could be caused by changes in diet in infancy and childhood.'

The link with diet is still contentious. The key suspect is salted food - both in one's ancestral diet and when fed to infants - and in particular a chemical compound called nitrosamine, a by-product of the preservation process. But as Chua says: 'We're not sure what specific diet component it is. We know that salted fish in the past was a problem; of course, these days the diet is changing, and it's especially given less to small children, which may be one reason there's been a decline in incidence in Hong Kong. There's been a similar pattern in Singapore.'

Moreover, says Dr Victor Hsue Chan-chee, specialist in clinical oncology at Hong Kong Adventist Hospital: 'The link with consumption of certain foods is not really proven. People say it's caused by salted fish congee and so on, but that's not yet supported by studies.' He thinks the decline in cases in Hong Kong could also be caused by a reduction in exposure to the Epstein-Barr virus, and by increased awareness of the disease among ear, nose and throat specialists and general practitioners.

However, says Ho: 'We teach medical students about it, but whether GPs can pick it up is another matter. The nasopharynx is in the middle of the head, so it's hard for a doctor to do an examination without referring the patient.'

He adds that the statistics also might not be completely reliable. 'We diagnose more for other cancers because we screen for them, so we think there are more of them. For NPC, there's still no common screening programme,' Ho says.

Considering its historical prevalence in Hong Kong, there have been very few public campaigns about the disease here. 'There's very little education coming from the government side,' Chua says. 'Most information comes from professionals and other organisations and societies. I'd say public knowledge is not very good, that's why so many present at such a late stage.'

Teo adds: 'We really need to reinforce the public health message. We have to drill into Hong Kong people's minds the idea of playing safe.'

Often the symptoms seem to have no known cause or are benign - but it's up to ENT surgeons to exclude malignancy, Teo says.

When NPC is detected, the first line of treatment is radiotherapy - with chemotherapy if the cancer is more advanced than stage one.

'Because the tumour is very deep inside and tends to grow into the bone and so on, surgery is not considered the first option,' Chua says. 'The first is usually radiation: NPC is more sensitive to it than other tumours.' In the past, long-term damage to surrounding sensitive areas was a problem, he says, but improvements in imaging technology mean that it's no longer a major issue.

Unfortunately, unlike many cancers, short-term lifestyle changes probably won't make much difference to the chances of you getting the disease. 'Any carcinogenic factors operating will cause cancer in only 20 to 30 years' time - there's a time lag,' Teo says.

Even smoking is less of a factor than you might think, unlike with many head and neck cancers; still, living a generally healthy lifestyle is the best way to reduce your chances of getting NPC or any cancer. And that includes avoiding salty and other preserved foods.

Fortunately, overall recovery rates are about 65 per cent - 'so we can say NPC, in general, is more curable than other cancers,' Teo says.

After four initial doses of chemotherapy and three back-up doses - plus 38 sessions of radiotherapy, all between November 2008 and March 2009 - To made a full recovery.

And he, at least, has brought away something positive from the experience.

'Before, I was kind of an anxious person, always angry, and I always put a lot of pressure on myself,' he says. 'Now I'm much happier. I choose to eat healthily, I go to bed earlier and I feel more relaxed.'

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- Percentage of NPC cases that present at the first stage (where there is a 90 per cent recovery rate)