When it was discovered that Tallulah had Cancer, and several very large, inoperable tumors, we also learned that the Cancer was a result of testing positive for Feline Leukemia.
Feline Leukemia is something most outdoor cats are susceptible to, and they get it from coming into direct contact with other Feline Leukemia+ cats. Well, our cats weren't outside cats, so we didn't know how Tallulah contracted it--she did go outside, but always only with a Human Escort and always for a short time.
But, since she was positive for Leukemia, we were worried the other three cats had become infected from her. But then we had houseguests and didn't want to get the other three tested--and perhaps getting bad news--while we had visitors, so we waited.
But, after a quick blood test and examination, all three of them came back negative for Feline Leukemia; and all three of them got jabbed with a Leukemia vaccine, just in case.
It was a long two-and-a-half weeks from Tallulah's passing to having the other cats tested but we were finally able to breathe easier.