Hayley, your female's brother might have been born with the oncogenic (cancer inducing) feline leukemia virus and if your cat harbored that virus as well would be at higher risk for developing a cancer. He may have been born predisposed to developing inflammatory bowel disease (IBD) and IBD can transmute into a small cell lymphoma in the GI tract. Your female could certainly suffer from IBD as it's relatively common in older cats but whether or not it would transmute into lymphoma is unknown. I would be pleased to review any additional information you could obtain from his owner. Please respond with further questions or concerns if you wish.
Yes, the vaccine against feline leukemia is quite protective and it's almost impossible to infect a cat of her age in any event. Please continue our conversation if you wish.
You're quite welcome.
Thank you for your kind accept. I appreciate it. You may receive an inappropriate follow-up from the site ostensibly sent by me. It wasn't and I apologize in advance should you receive it.