Can dogs smell cancer?

NYT reports excellent results of dogs trained to smell lung cancer. There are some minor objections, there certainly must be further investigation on larger groups of patients and healthy individuals published in respected journals, nevertheless, everybody admits that it worths closer attention.

However, when dogs can search for drugs, bombs and who knows what else, why couldn't they actually search for cancer? It would be cheap, sensitive, specific (in one word perfect) screening method, although wouldn't like to be irradiated on a dog's bark.