Hello Kat9606 - I have had breast cysts throughout my life. When I was younger I found cysts in my breasts (movable, somewhat painful - as they would pull on nerves I suppose). My doctors would aspirate them and they would go away. I also had a fibroid tumor removed about 30 years ago, benign. Lots going on in those breasts. I had a Stage 0 LCIS five years ago, diagnosed via micro calcifications, lumpectomy and clear margins - left breast. 3 years ago I developed a cyst in my right breast and it felt and looked just like a cyst and the doctors said I should just watch it....it was absolutely a cyst but I got worried and insisted on a closer look. During the ultrasound they found my Stage 1 lobular cancer under that cyst. I don't know how common that is but because I'd already had cancer (like you) it seemed like a good idea to check out the cyst anyway. An ultrasound is quick, painless and not terribly expensive and it saved my life. I don't want to panic you BUT........I would request that every odd lump or bump be checked.....I still do every time something seems out of the ordinary.
I had plenty of totally benign cysts and post mastectomy my pathology of the tissue in both breasts showed about every abnormality you can have....so my decision to remove my breasts (for me) was a good move. I had issues from the age of 18 with my breasts.
On the other hand.......my 30 year old daughter found a lump, went to her doctor and it was an oil cyst, completely harmless and it has now gone away.
Tough decisions - but for me.......double checking was a lifesaver and was not really supported by my oncologist (who isn't my oncologist anymore).
If you're worried, press for more information and don't be put off by any doctors who make you feel like you're over reacting. I hope your cyst is absolutely nothing.. Hugs!!