We lost our beautiful ten year old cat to intestinal lymphoma earlier this year. Her only symptom was vomiting, and we'd had her at the vet several times with this over the course of about ten months before pushing for further tests - £3K later and oh, actually, it wasn't just hairballs, it was a massive fuck off large cell cancer (the worst kind).
I think we were very unusual in that she never lost weight, never had any behavioural changes, and was absolutely never off her food, greedy to the very last. We opted to let her go "well" rather than pursue treatment that would have given her extra time but not cured her. She hated the carrier/car/vet and would have found it all incredibly distressing.
It broke our hearts but hopefully it was the right thing for her. I miss her so much.
We have since adopted a one year old boy from Cats Protection who is a little thug but an absolute joy. Last week he stole a pack of Dreamies during the night, ripped it open, ate the lot, and puked up. Today he wolfed his breakfast and threw up a small amount of food and a lot of grass.
My rational mind can see clear cause/effect here. My crazy mind is spiralling wildly that he too has cancer.
How often is your cat sick?