Most breast lumps are not cancer. Of all breast lumps that are biopsied, about 80% turn out to be benign. That said, a lump is worth understanding and getting checked, because the cause matters. Breast lumps can range from fluid-filled cysts and harmless growths to infections, hormonal tissue changes, and, less commonly, cancer.
Cysts
Breast cysts are fluid-filled sacs that develop within breast tissue. They’re one of the most common causes of a noticeable lump. Near the surface of the breast, a cyst can feel like a large, smooth blister. Deeper in the tissue, cysts feel harder because they’re covered by layers of breast tissue, which can make them seem more concerning than they are.
Cysts often grow larger and become sore just before your period, then shrink or feel less tender once your period starts. They can appear at any age but are most common in women in their 40s and 50s. A simple cyst seen on ultrasound almost never needs treatment unless it’s painful, in which case a doctor can drain it with a thin needle.
Fibroadenomas
Fibroadenomas are solid, smooth, firm lumps made of normal breast and connective tissue. They’re the most common solid breast lump in younger women, typically appearing in the teens through 30s. The classic feature is that a fibroadenoma feels rubbery and moves freely under your fingers when you press on it, almost like a marble sliding beneath the skin. They’re painless.
Most fibroadenomas stay small and don’t need removal. Some shrink on their own over time. Your doctor may recommend monitoring it with periodic imaging rather than removing it, unless it grows or causes discomfort.
Fibrocystic Breast Changes
Fibrocystic changes are the most common cause of generalized breast lumpiness rather than a single distinct lump. The tissue feels ropy, thick, or bumpy, and the changes tend to affect both breasts. The exact cause isn’t fully understood, but reproductive hormones, especially estrogen, play a central role.
The pattern is predictable: lumpiness and tenderness typically increase from midcycle (around ovulation) through the days before your period, then ease up once bleeding starts. This cyclical pattern is one of the strongest clues that your breast changes are hormonal rather than something more serious. Fibrocystic changes are not a disease and don’t raise your cancer risk.
Infections and Mastitis
A breast infection, or mastitis, can produce a lump that feels like a thickened area or a firm mass. It’s most common in women who are breastfeeding. Trapped milk in a blocked duct creates a breeding ground for bacteria, which can enter through small cracks in the nipple skin.
Unlike a painless fibroadenoma, mastitis comes with obvious signs of infection: the breast feels warm and tender, the skin turns red (often in a wedge-shaped pattern), and you may develop a fever of 101°F or higher. Mastitis typically responds well to antibiotics and improved milk drainage. If an area of firmness remains after the infection clears, your doctor may want to image it to confirm there’s nothing else going on.
Fat Necrosis
Fat necrosis happens when fatty tissue in the breast is damaged, usually from surgery, a seatbelt injury, a biopsy, or radiation therapy. The damaged fat cells form a firm, round lump that can feel almost identical to a cancerous mass on physical exam. It can also cause skin dimpling or retraction, which adds to the concern.
Fat necrosis is completely benign and doesn’t increase cancer risk. The challenge is that it often looks suspicious on a mammogram too, so a biopsy is sometimes needed just to confirm the diagnosis. If you’ve had any breast trauma or procedure and notice a new firm lump in that area weeks to months later, fat necrosis is a likely explanation.
When a Lump Could Be Cancer
Breast cancer lumps tend to be hard, irregularly shaped, and fixed in place rather than sliding freely under the skin. But there’s no way to tell from touch alone. Some cancers feel soft, and some benign lumps feel hard. What matters more is the combination of features surrounding the lump.
The CDC lists these as warning signs worth prompt evaluation:
- Dimpling, puckering, or thickening of the breast skin
- Nipple discharge that’s bloody or clear (and not breast milk)
- A nipple that suddenly turns inward or develops flaky, scaly skin
- Redness or irritation of the breast skin that doesn’t go away
- A change in the size or shape of one breast
A lump that doesn’t change with your menstrual cycle, keeps growing, or appears alongside any of these signs deserves imaging sooner rather than later.
How Breast Lumps Are Evaluated
Evaluation usually starts with imaging. For women under 30, ultrasound is typically the first step because younger breast tissue is denser and harder to read on a mammogram. For women 30 and older, a mammogram is usually the starting point, sometimes followed by ultrasound for a closer look.
Dense breast tissue makes mammograms less sensitive, meaning they’re more likely to miss a cancer. If you’ve been told you have dense breasts, your doctor may recommend supplemental screening, though the best approach for additional imaging is still being studied.
After imaging, radiologists assign a standardized score that guides what happens next. A score of 1 means the result is normal. A score of 4 means the radiologist sees something concerning enough to recommend a biopsy, with the estimated likelihood of cancer ranging from as low as 2% to as high as 95% depending on the subcategory. A score of 5 means the finding has at least a 95% chance of being cancer and a biopsy is strongly recommended.
What Happens During a Biopsy
If your imaging results call for a biopsy, the type depends on what the lump looks like and where it is.
- Fine needle aspiration: A very thin needle is inserted into the lump to withdraw a small sample of fluid or tissue. No incision is needed. This is often the first step when the lump might be a cyst, because draining it can be both diagnostic and therapeutic.
- Core needle biopsy: A larger needle removes small cylinders of tissue from the lump. This also requires no incision and provides more tissue for analysis than fine needle aspiration.
- Surgical (open) biopsy: A cut is made in the breast to remove part or all of the lump. This is less common now that needle biopsies are widely available, but it’s sometimes needed when needle results are inconclusive.
For needle biopsies, you can typically return to normal activities quickly, though you’ll likely be told to avoid strenuous exercise for a few days. Bruising and mild soreness at the site are normal.
Routine Screening Guidelines
The U.S. Preventive Services Task Force recommends that all women get a screening mammogram every two years starting at age 40 and continuing through age 74. This applies to women at average risk, even those with no symptoms or family history. Women with higher risk factors, such as a strong family history or known genetic mutations, may need to start earlier or add MRI screening.
Finding a lump between scheduled screenings doesn’t mean you should wait for your next mammogram. A new, distinct lump that persists for more than one full menstrual cycle warrants evaluation on its own timeline, regardless of when your last screening was.