Q: What are breast cysts?

Answer: Breast Cysts tend to occur in women aged between forty and sixty, but again we see them at other ages too. They are fluid collections within the breast and are probably due to a combination of changing hormone levels and increased sensitivity of the breast tissue to those hormones. Cysts often come up quite quickly and it is common for them to appear, literally, overnight. They are often round in shape and can be a little bit tender too. Large cysts can be drained with a small needle to remove the fluid. Smaller cysts will often go away on their own, although they can cause a fair bit of discomfort in the breast.

-- See full article by Consultant Breast Expert, Mr Simon Marsh, I have a breast lump, what should I do?