Cysts, benign tumor. In my surgical practice, the most common cause of a well-defined breast lump is a cyst. This can easily be differentiated from a tumor by ultrasound or needle aspiration. If the lump is solid, it may be due to a benign tumor (ie, fibroadenoma) or a cancer; the only way to determine this is by tissue diagnosis, which can usually be done by needle-biopsy in the office or breast center.
Breast Lump. Nine out of ten breast lumps are benign and may represent common conditions such as fibrocystic disease, benign fluid filld cysts, and benign tumors known as fibroadenomas.
Many things. While cancer is the most serious breast lump, there are many other causes. The breast is naturally lumpy, as the glandular structure is built like a branching tree. Fibrocystic changes cause lumps. Cysts cause lumps. Benign tumors like fibroadenona cause lumps. Regardless, any new lump should be viewed with suspicion for cancer. See your physician. You may need a biopsy.