Dear Mandible, When doing a breast self-exam (BSE) what you are looking for is a lump that stands out as different from the rest of your breast tissue. Becoming more familiar with your breasts by doing BSE each month will help you tell the difference between your normal
The simple answer is that you can't tell the difference between a cyst and a malignant tumour. Only a pathologist can differentiate. A cyst can be aspirated by a nurse/technician or doctor, but a biopsy is the only way to tell if a mass or lump is malignant. Well, that's what my surgeon told me, for what it is worth.
I found a mass in my breast and it was very easy to tell that it felt different than any other area. I had always wondered if I woould be able to tell but when something was there, it was very easy to feel. I hope this helps