It is not entirely clear from your question where exactly this cyst is located. Since you do mention nursing, I will assume that the cyst is on the breast. Most cysts, especially if they have been present for 20 years without any significant change or growth, are likely to be benign and probably do not require any treatment. However, you should show the area to your primary care doctor
or your OB GYN doctor, who can more fully examine the area and help you decide whether or not something needs to be done.
Occasionally, if cysts are very large or uncomfortable, they may need to be surgically removed. Again, this is something that your doctor can discuss with you. Most of the time, if it is necessary to remove a cyst, this is something that can be done in just a few minutes as a minor office procedure using just local numbing medication injected into the skin. Some primary care doctors
do their own minor office procedures like this, whereas others may refer you to see a general surgeon
to have the procedure done.
Again, please discuss this issue with your OBGYN.