Tracy:

              supernumerary breast tissue or polymastia occurs along the milk
line and is believed to be casued by a failure of the mammary ridge to undergo
a normal regression.

                ectopic axillary breast tissue is believed to be a  variant of
supernumerary breast tissue,... but it  is commonly bi-lateral.

                 it will react to the same hormonal stimulation as breast
tissue as this is what it is...

                Patricia