Most breast lumps are not cancer. About 90% of new breast lumps turn out to be benign, meaning they’re caused by something harmless like a cyst, a hormonal change, or a noncancerous growth. That doesn’t mean you should ignore a lump, but it does mean the odds are strongly in your favor. Understanding the most likely causes can help you figure out what you’re dealing with and what to expect if you get it checked out.
The Most Common Causes
Several benign conditions can create a noticeable lump in your breast. What you’re feeling likely falls into one of these categories:
- Cysts: Fluid-filled sacs that can feel smooth and slightly squishy, almost like a grape under the skin. They often become tender or more noticeable right before your period. Cysts are most common in premenopausal women and in those taking hormone therapy during menopause.
- Fibroadenomas: Solid, round lumps that feel firm and rubbery. They tend to move easily when you press on them. Fibroadenomas are the most common benign breast tumors in women under 30, though they can appear at any age. They may grow during pregnancy when estrogen levels rise and shrink after menopause.
- Fat necrosis: A firm, usually painless lump that forms after the breast has been injured, had surgery, or received radiation. The skin around it may look red, bruised, or dimpled. This is simply damaged fatty tissue, not a sign of cancer, though the dimpling can understandably cause alarm.
- Fibrocystic changes: Areas of lumpy, rope-like texture in the breast tissue that come and go with your menstrual cycle. These tend to flare up between ovulation and the start of your period, then improve once bleeding begins. Reproductive hormones, particularly estrogen, are thought to drive these changes.
Hormonal Lumps That Come and Go
If the lump you’re feeling seems to change size or tenderness throughout the month, hormones are the most likely explanation. Many women notice their breasts feel lumpier, more swollen, or sore in the two weeks leading up to their period. This is normal. The tissue responds to rising and falling levels of estrogen and progesterone, which can cause temporary swelling and fluid buildup.
A helpful test is to track the lump across one full menstrual cycle. If it shrinks or disappears after your period starts, it’s very likely a hormonal change or a simple cyst rather than something that needs treatment.
Lumps During Breastfeeding
If you’re nursing, a hard or painful lump could be a blocked milk duct, which usually resolves on its own with continued feeding, warm compresses, and gentle massage. But if the area becomes red, hot, and swollen, and you develop a fever or feel generally unwell, that suggests mastitis, an infection of the breast tissue. Mastitis can progress quickly in a lactating breast because stagnant milk and the loose tissue structure allow infection to spread. If left untreated, it can develop into a breast abscess: a well-defined, painful, fluctuant lump that may need to be drained.
Signs That Warrant a Closer Look
You can’t reliably tell whether a lump is cancerous just by feeling it. That said, certain features are more common in benign lumps versus concerning ones. Lumps that feel smooth, move freely under your fingers, and change with your cycle are more likely benign. Features that prompt doctors to investigate further include a lump that feels hard or irregular in shape, doesn’t move when you push on it, or keeps growing over weeks. Skin changes like dimpling, puckering, or thickening over the lump also warrant attention, as does nipple discharge (especially if it’s bloody or comes from only one breast), or a newly inverted nipple.
None of these signs automatically means cancer. Fat necrosis, for example, can cause dimpled skin that mimics a malignant lump. But these are the features that tell a clinician imaging or a biopsy is the right next step.
What Happens When You Get It Checked
A clinical breast exam is the starting point. Your provider will look at both breasts while you sit and lie down, checking for differences in size, shape, skin texture, and nipple appearance. They’ll press through the tissue systematically, noting the lump’s size, shape, texture, and whether it moves. They’ll also feel under your arms and near your collarbone for swollen lymph nodes.
From there, the next step is usually imaging. For women 40 and older, that typically means a mammogram. For younger women, an ultrasound is often preferred because denser breast tissue makes mammograms harder to read. Ultrasound is also useful for determining whether a lump is solid or fluid-filled, which immediately narrows the possibilities. If it’s a simple fluid-filled cyst, that alone may be enough to confirm the diagnosis.
If imaging raises any questions, a biopsy comes next. The two main types differ in what they can tell you. A fine-needle biopsy uses a thin needle to extract cells. It’s quick, requires no anesthesia, and causes minimal discomfort. However, its accuracy varies widely, with sensitivity for detecting cancer ranging from 35% to 95% across studies. A core-needle biopsy uses a larger needle under local anesthesia to remove a small cylinder of tissue. It’s more accurate, correctly identifying malignant lesions about 96% of the time compared to 67% for fine-needle methods. It also provides more information about the biology of any abnormal cells. Complications from either are uncommon, though bruising and soreness are slightly more frequent with a core biopsy.
Lumps in Men
Men can develop breast lumps too, and the most common cause is gynecomastia, an increase in breast gland tissue driven by a hormonal imbalance between estrogen and testosterone. It can happen naturally during puberty, in older age, or as a side effect of certain medications including anti-androgens, anabolic steroids, some antidepressants, opioids, and anti-anxiety drugs. Alcohol, marijuana, and heroin use can also trigger it. The swelling is usually centered behind the nipple and may feel tender, especially in teenagers.
Male breast cancer is rare but real. Warning signs in men are similar to those in women: a firm or hard lump (rather than the soft, even swelling of gynecomastia), dimpled skin on the breast, or discharge from the nipple. These warrant the same evaluation process of imaging and possible biopsy.
Screening Between Lumps
The U.S. Preventive Services Task Force recommends mammograms every two years for women aged 40 through 74. This is routine screening for people with no symptoms. Finding a new lump is different from screening. If you feel something new or unusual, that’s a reason to be evaluated regardless of when your last mammogram was or how old you are.