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 routine screening like your annual mammogram.

A breast tumor, on the other hand, results from cancer cells dividing and growing uncontrollably in your breast and can have many causes, like lifestyle factors or damage to your genes. 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.

1. 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.

Cause of breast cancer and how the cancer appears varies 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
• Family history of breast cancer
• Early menarche and late menopause
• Lack of physical activity
• Alcohol consumption
• Higher body weight

Breast cells become cancer cells after mutations (changes) in genes occur. Right now, we 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 experts haven’t been able to identify.

2. 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.

Breast tumors can form in several different parts of the breast tissue. Sometimes, they first appear as an abnormal lump, but they may not always show up as a lump you can feel. Some breast cancers will first appear as an abnormal lump in your breast, while others feel like a lump later as the cancer develops.

The MD Anderson Cancer Center points out that 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.

3. Cysts and Tumors Change Differently Over Time

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 and start out as small sacs, per the American Cancer Society. 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 their 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.

Tumors almost always require some sort of treatment, such as chemotherapy, radiation, or surgery. If left untreated, the cancer cells will continue to grow, resulting in worse outcomes.

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, the best thing to do is 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. If you have a lump that is not 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 breast 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 health care 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 ensure the cells are benign (not cancerous). Additional imaging tests like an 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 is not usually necessary. If a cyst is causing you discomfort, it can be drained using a small, fine needle to remove the fluid. Sometimes, you can 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 can also express a protein called HER2 that is 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 you have, you can receive chemotherapy or a specific therapy like hormone therapy. After the treatment regimen, your doctors will take an image of your breast to ensure the tumor is completely gone.

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

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 65,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you noticed a lump in your breast? Share your experiences in the comments below, or start a conversation by posting on your Activities page.