Kumquat and Quincy were foundlings from a farmer's haystack in 2001. Kumquat ran onto the road and was hit by a car in 2005 but I rushed him to the hospital and they kept him there and after many operations and three months I picked him up. He seemed as good as new, running and sliding on the kitchen floor to show off. He would jump into your arms or up on top of furniture (as pictured) and pose to show how good he was doing. Everyone loved him and couldn't resist holding him.
In 2013 he just fell off the sofa with a thud and I rushed him to the vet's office. They told me he was critically ill with diabetes and would not recover. I allowed them to put him to sleep. Everyone that knew him cried. Quincy lived till 2017. Quincy's photo is in my batch of photographs taken as he was sneaking under the chicken wire garden fence.

I'm sure they had really good lives with you. It's hard to do that responsible pet owner thing at the end. I last had to do it in early 2016 and cried my eyes out. But it's part of being a pet parent.

I have one left. She was born in 2001, so is getting up there in years. She has diabetes. She's been getting two insulin shots daily since 2009. Expensive since I didn't purchase pet insurance for her. But she's totally worth it.

The last time I had her at the vet, they told me she has a mass in her chest. Likely either lung cancer or lymphoma. I decided to leave it alone. She's 17-years-old and asymptomatic for it thus far. She wouldn't understand the whole biopsy/surgery/chemo/ radiation thing. It would just be torture as far as she was concerned.

@vita I truly understand how you feel about taking care and staying with her. A very long time ago, the mother of many of my cats developed cancer and I waited until she showed me her pain before I took her in for the "service". I held her hand and talked to her.
I hope you can go through with it as painlessly as possible.
My heart is with you.