Before your heart sinks too low about the lump you found in your breast, know there are plenty of harmless reasons you might feel one. The American Cancer Society lists many benign (noncancerous) breast conditions that may cause a lump.

Breast cysts are among the most common causes of breast lumps. These fluid-filled sacs can be small or large and could be accompanied by symptoms including nipple discharge or pain. However, some breast cysts don’t have any symptoms and are discovered incidentally during a routine screening, like your annual mammogram.

A breast tumor, on the other hand, results from cancer cells dividing and growing uncontrollably in your breast. Sometimes, a tumor feels like a lump, and sometimes, it’s only found on a mammogram.

A cyst and a tumor are distinct conditions. This article covers six key differences between a cyst and a tumor, including how they feel.

1. Cysts and Tumors Feel Different

A breast cyst and a breast tumor can both feel like a lump in your breast. Cysts can feel round and might be tender (or sore) to the touch. You might feel a specific lump, or your whole breast might be sore or swollen.

Most tumors aren’t painful, whereas people often do notice breast cyst pain. As they grow, cysts press on surrounding breast tissue, and that can cause pain or discomfort.

One MyBCTeam member described the surprising discomfort they felt upon finding a breast cyst: “Found a cyst, they said it’s nothing. The pain is so intense.”

Breast cancer can begin in different parts of the breast, including the ducts, lobules, and surrounding tissue. Sometimes, the first sign is a lump you can feel — but not always. Some breast cancers develop without forming a noticeable lump at first and may be found through imaging tests like a mammogram. Others may feel like a lump as they grow. Some types of breast cancer tend to grow slowly, while others can be more aggressive and spread quickly.

A MyBCTeam member described how quickly the lump they felt in their breast grew: “I found the lump while showering. They thought it was a small, marble-sized lump. After my lumpectomy and pathology and PET scan, it was the size of a plum, and the cancer had metastasized to my bones and liver.” (A PET scan — short for positron emission tomography scan — is an imaging test that helps doctors see how tissues and organs are functioning.)

2. Cysts and Tumors Have Different Causes

Breast cysts don’t have a clear cause, and they don’t share the same risk factors as breast cancer. They’re often driven by normal hormone changes during a person’s menstrual cycle and are most commonly diagnosed in women who haven’t reached menopause, according to The University of Texas MD Anderson Cancer Center.

Many cysts are a result of fibrosis in the breast, which is thickening and changes to the cells that make up your breast tissue. When these cells break down and change shape, a fluid-filled cavity can form.

Importantly, a breast cyst doesn’t increase your risk of getting breast cancer later.

Causes of breast cancer and how cancer appears vary from person to person. Identifying a single cause or even a group of causes of breast cancer is difficult. Instead, certain risk factors might increase your chances of developing breast cancer.

Some risk factors for breast cancer include:

• Older age
• Genetic mutations (changes)
• Family history of breast cancer
• Early menarche (first menstrual period) and late menopause
• Lack of physical activity
• Alcohol consumption
• Higher body weight

Breast cells become cancer cells when mutations in genes drive uncontrollable growth. Right now, scientists know about only a few genes typically mutated in breast cancer, which can be inherited (passed down within families). About 90 percent of breast cancers develop from an acquired gene mutation (one that isn’t inherited), which health experts haven’t been able to identify.

3. Cysts and Tumors Both Change Over Time — in Different Ways

Breasts go through normal changes over time. For example, your breast could feel swollen or tender before your menstrual period. There can be extra fluid in your breast at this time that feels like a lump. Similarly, during pregnancy, the milk ducts in your breast grow in preparation for breastfeeding.

If you notice a lump that feels swollen or tender before your menstrual cycle starts but goes away after a few days or weeks, it could be a breast cyst. They’re most common in women in their 30s and 40s, according to The University of Texas MD Anderson Cancer Center. Cysts start out as small sacs. Over time, fluid can build up, and the cysts will grow.

The American Cancer Society notes that a cyst can also get bigger with a woman’s monthly hormone changes. For example, some cysts are noticeable before the menstrual period but get smaller later in the cycle. Other times, cysts are recurrent, meaning they go away and come back.

Some people mention that certain foods, like caffeine, can worsen symptoms like pain or swelling. However, there is little research establishing a clear link between food stimulants and breast symptoms.

A breast tumor can appear with no obvious indicator, such as your menstrual cycle or becoming pregnant. Breast tumors are also unlikely to go away after a short time. They’re also diagnosed more in older women, per the Centers for Disease Control and Prevention (CDC).

4. Cysts and Tumors Are Not Equally Dangerous

Simple breast cysts are often no cause for concern. They might go away on their own. If your doctor diagnoses you with a simple cyst and you are not bothered by pain, then they typically won’t perform a treatment.

Most tumors need some form of treatment, such as surgery, chemotherapy, or radiation therapy. Without treatment, cancer cells may continue to grow or spread, which can lead to worse outcomes later on.

If you notice a lump of any kind, the best thing to do is to contact your doctor and ask if you need to go for screening. Because a lump could indicate a tumor, it’s a good idea to rule that out with an imaging test or breast biopsy.

5. Cysts and Tumors Look Different on Imaging Tests

Both cysts and tumors can show up on a routine mammogram, but they look quite different during the scan. If you have a lump that isn’t cancerous, it’s often smooth and round. It also has clear edges. These types of lumps are often cysts.

Breast tumors look irregular and jagged on a mammogram. Typically, tumors have less clear margins — the boundary between the healthy breast cells and the cancer cells.

Tumors can also be accompanied by other changes in the breast, like dimpling of the skin, nipple discharge, and changing size or shape of the breast as the tumor grows.

Your healthcare provider can tell the difference between a cyst and a tumor on imaging tests. They will let you know if you need to have additional testing, like a biopsy, to find out whether the cells are benign or cancerous. A biopsy involves removing a small sample of tissue so it can be examined under a microscope.

Additional imaging tests, such as ultrasound, can also distinguish between a cyst filled with fluid and a solid breast tumor.

6. Cysts and Tumors Have Different Treatments

Breast cyst treatment isn’t usually necessary. If a cyst is causing you discomfort, it can be drained using a small, fine needle. Some people have recurrent cysts that can be removed by surgery. If your doctor diagnoses a cyst and it’s not bothering you, you don’t need treatment.

The treatment for a breast tumor depends on several factors, such as the hormone receptors your breast cancer has. Breast cancers can express the estrogen receptor and/or progesterone receptor. These can be targeted with specific drugs to treat the cancer. Breast tumors that express a protein called HER2 are also treated by specific medication.

Most people with breast cancer will receive local treatments, like radiation therapy and surgery, to remove the tumor. Then, depending on what kind of breast tumor they have, they may receive chemotherapy or a specific therapy like hormone therapy.

After you complete your treatment plan, your doctor may order imaging — such as a mammogram, ultrasound, or MRI — to see if the tumor is gone or if more treatment is needed.

Early Detection Is Key

The American Cancer Society recommends regular screening — by a physical exam or by imaging tests — for all women, especially those over 45 years old. Because a breast lump could be a tumor, it should never be ignored. Detecting cancer early gives you the best chance of eliminating the cancer before it has a chance to spread within your body.

Talk With Others Who Understand

On MyBCTeam, people share their experiences with breast cancer, get advice, and find support from others who understand.

How have you dealt with your breast cyst or tumor diagnosis? Let others know in the comments below.