I've only had chickens since 7/2015, so I'm new to all this. I lost one hen a few months ago that had a huge softball size tumor on her upper chest. She was a Silkie. Now I'm noticing several of my Showgirl hens and one of my Silkie roosters have one too now. Their's are about the size of a small egg to a plum. The person I bought them all from said they'd bought them from top breeders and they were supposed to have had all their proper shots. I feed them Purina pellets and they get fresh veggies and/or fruits daily. I make my own treat mix too. I need incite on what could be going on with them. Thank you for any help you can give me.