A suspicious lump in your breast should be checked by your doctor. Aside from an extensive physical examination, the doctor will also want to do a mammogram - a low-level X-ray that can show abnormal areas in your breast. An ultrasound can sometimes be performed to see if the lump is a fluid-filled cyst or a solid growth. Even if the lump which can be felt is not visible on the mammogram, some sort of biopsy may need to be done.

Using a needle, fluid can be removed from a cyst to check if it contains cancerous cells. A solid lump must be analyzed under a microscope. This requires either a needle biopsy or a surgical biopsy to be performed, to remove some or all of the lump.

Cancerous cells can be tested for the presence of estrogen- or progesterone-receptors. Other tests - including a chest X-ray, bone scan, and liver function evaluation - are conducted to help the doctor determine whether the cancer has spread.