Hi. Thanks for the question. Yes, worms can make a cat's stomach swell but there are many other things that can also cause the swelling. Risk factors would include fleas and if he goes outside. Usually its the younger cats that get worms. I would like some more information.
Is he vomiting?
Does he have diarrhea?
Is he drinking and urinating normally?
Does he eat well?
Are there other cats around him?
I will look for your reply.
If possible have a veterinarian look at a stool sample to see if there are worms in his stool. If not, I would recommend an x-ray because a tumor could be causing the swelling as well, especially if he is having trouble breathing as you say. A tumor could be putting pressure on the chest making it difficult for him to breathe.