Yes, any mammal can get breast cancer. Males as well as females can get it as well. Actually, my grandpa had breast cancer.

Many tumors are not cancerous, however.

My niece's male guinea pig got mastitis. Yes, even males can ... I didn't know that before. His symptoms sounded a lot like this guinea pig's.

The only way to be for sure is to take him to the vet for a checkup and examination.

http://www.provet.co.uk/Guinea%20pigs/guineapighome.htm