My flock is only 2 weeks old and all appear healthy, except the sweetest one. She had some constipation trouble early on which cleared up. She eats and drinks. She's the fastest runner and the best flier. She's also the smallest and doesn't seem to be feathering out like the others, although her wings are quite developed. On her right breast she has what appears to be, and feels like a tumor. It's definitely getting larger, about the size of a shooter marble now. Her whole body fits in the palm of my hand. It doesn't seem to be slowing her down. None of the other chickens seem affected, nor do they pick on her. She has been vaccinated for Marek's. Could this be a cyst associated with the vaccination? Could it be a symptom of runting syndrome? I found a vet 70 mi from here who'll see her, but I don't want to put either of us through that unnecessarily. She's so sweet-- a perfect lap chicken. I don't want to lose her.