Should an old dog be treated for cancer?

I have a 13 year old dog with three tumors. One on her hind leg has started bleeding. Should an old dog be subjected to agressive treatment like surgery and chemo?
Thanks everbody for your responses. We met with the vet yesterday and we determined that the dog was not a good candidate for surgery due to her age and a heart murmer. Sadly, we had to put her down.