I take a rather odd comfort that it's an exceedingly rare lymphoma, and that cancer rates are already much lower in beagles than most other breeds, meaning that Gir died as bizarrely as he lived. You hate to think that something normal got him.
He was, if I'm being honest, not exactly a good dog--he was incontinent, largely untrainable, deafeningly loud, food-aggressive and prone to casually chewing holes in himself. His health issues were legendary and his pill case was bigger and more complicated than mine (and his pills substantially more expensive.) But he was cheerful and generally good-natured and we loved him dearly, and he lived so long with bits falling off that we started to wonder if he was the harbinger of some kind of canine zombie apocalypse.
"Ah, Gir," said the vet at the end. "Genetics weren't in your favor." And lord, they weren't, but he lived halfway to forever anyway.