Question

My cat, Simon age 7, was euthanized yesterday after the following events:For the previous three days he had stopped eating and was not sleeping (I would find him sitting in the living room in the middle of the night when he usually slept).The day before yesterday I noticed he was doing what has since been described to me as abdominal breathing. I brought him to the emergency vet yesterday.I was told after an x-ray that he had a lot of fluid in his lungs, indicating heart failure, cancer or some fatal virus. After his lungs were drained and the cells were looked at (not by a pathologist), it was determined that he had cancer, probably lymphoma. Simon was an indoor cat, but he always got his feline leukemia shots. I was told chemotrherapy does not work on cats and he should be euthanized. I have since seen some on-line articles indicating that feline lymphoma is often caused by the feline leukemia virus. Are there other causes since Simon was vaccinated? Did he have to be euthanized?