I didn't know that guinea pigs were prone to tumors. My intact female was 3 years old when we brought her to the vet because she had 3 large tumors in her stomach area. One was starting to get infected. The vet started her on antibiotics and pain meds. We couldn't just let her go...she had surgery that cost us over $600.00, and thank God when the Vet biopsied the tumors, they were not cancer...they were fatty tumors. It's been a year now, and Emily is a happy and healthy part of our family.