A lump in the breast can be caused from a cyst, an infection, breast tissue, a benign (non cancerous) tumor, or a malignant (cancerous) one. A lump in the breast does not equal breast cancer.
Likewise not all breast cancer comes in forms of lumps, so it's important to also look at your breasts to notice any change in the nipple or skin, any discharge, or any difference of sensation (itching, burning, pulling, etc.).