What most naturally follows?

How to diagnose canine cancer 
Look for lumps on the skin. 
The most important thing you can do is to be alert for changes in your dog. This includes paying attention to lumps, like watching for the growth of a new lump on the skin, the enlargement of an existing lump, and a change from a lump not bothering the dog to becoming angry-looking or itchy.
Watch for unexplained weight loss. Another common symptom of canine cancer is weight loss.