Our nine-year-old was given a Wii computer game for his birthday. About a week later, he began to complain of a pain in his shoulder, and of being very tired. Could the game be the cause?

Yes. Believe it or not, there are reports of 'Wii shoulder' in the medical journals. He has simply started using muscles that he hasn't used much before. If he stops playing the game for a few days, the pain will disappear. I had to deal with similar shoulder pains and upper chest muscle pains in a 45-year-old man and his 16-year-old son after they started to play golf in the new year. They had spent hours hitting balls on a driving range and thus suffered a similar distribution of muscle strain. It subsided after they changed their practice habits.

Could a person have had an untreated cancer in any part of the body for 15 years without it spreading?

It is possible with some slow-growing cancers that tend not to spread. It happens, for example, with some skin and breast cancers. However, it is rare. Most cancers should be treated as soon as they are suspected. I'm curious, though, as to why you asked this question. Have you just been told you have cancer, and suspect that you have had it for many years? If so, that's very unlikely. Many people tend to date their illness from some past event, such as an accident or an emotional crisis, that is usually a coincidence. If that is what you are doing, forget it. Cancers usually arise out of the blue, with no obvious precipitating event.

Do you have a question for Dr Smith? Email doctordoctor@theguardian.com