Is it possible to transplant mammary gland in an amastia patient?

Unlikely: When you say possible, it is a stretch. Not likely to happen due an imbalance in the risk of immunosuppression, and the benefit to have it done. This would trump the technical challenges of even attempting to do this.

Possible, yes....: As mentioned the problem of rejection is big with this kind of transplant. Much better to perform reconstruction with better outcomes and less risk.