cat eating and losing weight

I feed outdoor cats and one began having rapid weight loss, but a huge appetite. I took him to the vet and did blood work, stool check, everything was neg. The vet said it was cancer. I brought him inside and gave fluids and did what I could for him until the end.
Now another cat has the same symptoms. So now I am wondering if the first cat really had cancer or something else. I am taking the second cat to a different vet. I don't want to lose a second cat. If you have any ideas what this could be please let me know. Thank you.

the at i just rescued from the veterinary clinic I work at has been doing the same thing since moving in with me. I took him back to the clinic and had the same doctors who had placed his feeding tube when he was unable to eat check him out. (he was hit by a car and surrendered because the previous family just didnt care enough to treat him) I would recommend taking him to the vet and having a feline wellness panel ran. Its a blood test that is sent off to the lab but it checks the organ functions as well as the thyroid because hyperthyroidism is common in cats. If the cat is over 8 you should ask for a senior wellness panel instead which is a blood test geared more toward cats that are middle aged.

Here is what my book says: This could be related to parasites, kidney disease, diabetes, or even cancer. Any sudden change in weight needs to be checked out by a vet.

I agree with treelf - if the vet didn't do a thyroid test, that's the next thing you should try. Weight loss and a big appetite are classic symptoms of thyroid trouble, so you want to look into that possibility. There are several thyroid tests that are run off the same blood sample for accuracy called T4, Free T4, T3. Make sure your vet does those (some only run one).

Best of luck to you and your cat- hope it will turn out to be something that's easily treatable. Please let us know how he's doing.

My cat is 10. They did do a thyroid test. He is down to 8lbs and is normally about 11lbs or so. He had a fast heartbeat and a murmur. I didn't know about the different tests so I will have to ask. I just have to wait for the results.......... He is such a great cat. I don't want to lose him. Thanks for all your replies.