It is better for medically trained people to make medical diagnoses, however, a visible or palpable tumor would be a noticeable symptom of cancer.
By taking him to a veterinarian for an exam.
Yes, there are many ways your vet can test for cancer.
There are many different treatments for cancer in dogs and it really depends on what type of cancer it has. If it is lymphoma (the most common type of cancer in dogs) depending on which treatment...
Any dog could get cancer, Female dogs can have breast cancer just like humans.