It's disconcerting to find a soft lump in your breast. You may wonder, "Is this breast cancer?" While you should be alert to all changes in your breasts, know that finding a lump doesn't necessarily mean the worst. Breast cysts, fluid-filled sacs that most women discover during a self breast exam, are common. These cysts form when an overgrowth of glands and connective tissue block the milk ducts in the breast, causing them to dilate and fill with fluid. Usually, cysts are round or oval lumps, with the soft texture of a water balloon. It's common for them to grow larger just before a woman's period, or to shrink after menstruation ends. Occasionally, patients report pain or tenderness around the area of the cyst. Whatever the specific symptoms, cysts most often occur in perimenopausal women in their 30s and 40s. The good news is that just one in 1,000 of them contain a tumor - and in almost all of these rare cases, the tumor is benign, or non-cancerous. Still, it's a normal reaction to be concerned if you find a breast lump, and it's smart to visit your gynecologist and get it checked out. Generally, she'll ask about the cyst's history and perform a clinical breast exam. Your doctor may also order a breast ultrasound, which allows her to better analyze the lump and determine if it's fluid-filled. If the lump is solid inside, your doctor might order further tests, like a biopsy, to ensure that it's not cancerous. Sometimes a doctor will perform a fine needle aspiration on the cyst, or remove it surgically. Aspiration involves inserting a needle into the breast lump to draw out fluid. Aside from ensuring that the lump is nothing more than a cyst, aspiration helps to deflate growth, essentially treating the cyst. If the fluid that emerges from a cyst is bloody, however, it must be sent to the lab for further testing. Your doctor will want to rule out the possibility of cancer with additional tests if no fluid emerges, since that can suggest that the lump, or a portion of it, is solid. Breast cysts are usually no cause for concern, but you should always discuss any changes in your breasts with your doctor.