A cyst is a fluid-filled structure and by definition is benign. A complex cyst is also fluid filled, but has solid structures (walls or septations) within the cyst. The concern with a complex cyst is whether the solid components might (rarely) be malignant. Also, complex cysts can be more difficult to aspirate, since the areas of fluid may be separated into compartments. If there is concern, a biopsy can be done.
A solid lump can be a fibroadenoma, which is also benign, or some other abnormality, including cancer. Sometimes radiologists will recommend close follow-up (3 or 6 mths) of a solid lump if it does not have an obviously suspicious appearance, to see if it grows or changes, but the only sure way to determine what a soid lump is, is through biopsy.
Best wishes...
A fluid filled lump is a cyst. If it becomes bothersome, it can be drained. A hardened lump could be just dead tissue, an enlarged or infected gland, or breast cancer. Only examination by your doctor, with a mammogram and ultrasound will give you an idea of what it is, and a doctor would probably want to do a fine needle biopsy just to be sure whether it is cancer or not. 80% of lumps are benign.
I am a 3yr cancer survivor, bilateral mastectomy, 2 rounds reconstruction. No chemo, no radiation, oral chemo will total 5 years. Side effects difficult but doable. No hair loss, some weight loss....new perky boobs!
Get in to your doctor right away....to either put your fears aside, or to address the issue head on. I will do all I can to help you should you need it.