Sorry about your loss of Max, Sam; it's tough losing a long-time family member. Especially as one has responsibility for making momentous decisions.
A year ago our Cinnamon had a lump growing on her thigh that was found to be a cancerous tumor. The local vet removed it, but several months later it had grown back. We took her to a university veterinary teaching hospital several hours' drive away, every week for a while for radiation and chemo-therapy. Fortunately, she's now in remission, at age 16 safe for a while anyway!