Can a cyst grow bigger under skin? tenderness and aches around and spreading out from cyst under armpit and into breast but no visible inflammation.

Yes: Hi Marsha, Yes it can. "Cyst" is somewhat of a general term as there are many types of cysts. By your description, you may have an infected cyst if you are having tenderness/pain and it feels like it is enlarging. Sometimes infections that are deeper will not clearly show much redness over the skin. It may be worthwhile getting it examined by a physician. Hope you feel better soon!