Hello, and I hope I can help you today. Is understandable to be nervous about having a lump in your breast at any age. You are correct in your knowledge that breast cancer under the age of 30 is extraordinarily rare, however any lump in the breast that is present for more than short period of time really should be evaluated. It is not recommended that mammograms be performed in women who are breast-feeding because the calcium in your milk can sometimes cause abnormalities on the mammogram that mimic cancer. However ultrasound, a diagnostic test similar to that which are baby got while you are pregnant, can be performed on your breast to see if the lump is the cyst, or a solid mass. A specialist in diseases of the breast would be a reasonable person to see for this evaluation if your GYN doctor is not willing or able to properly examine you and refer you for the ultrasound. However, I do want to reassure you that most palpable lumps found in women who are pregnant or breast-feeding are due to some clogging or other issues of the milk glands and are rarely associated with cancer. I hope that I was able to adequately answer your question today, and that my advice was reassuring. Best wishes and good luck, Dr. Brown