Can an Armpit Lump Be a Symptom of Breast Cancer?

An armpit lump—or axillary lump—can occur as a symptom of many conditions that range from harmless to serious. It is often the result of an enlarged lymph node.

While it is a common symptom of breast cancer, an armpit lump is also linked with infections, cysts, skin problems, and other factors like antiperspirants.

Many armpit lumps appear and then go away after a few days. Pain may or may not be present. An armpit lump that is hard and doesn't change should be checked by a healthcare provider.

This article describes when an armpit lump could be a symptom of breast cancer, the causes of an armpit lump, when to see your healthcare provider, and the types of treatment used.

armpit lump

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What Is an Armpit Lump?

An armpit lump is an enlargement or a swollen bump that develops in the area where the underside of your arm joins your shoulder. It usually develops deep beneath the skin.

An armpit lump can vary in size, texture, and impact on arm mobility. Pain may or may not be present depending on the position of the lump.

In most cases, an armpit lump occurs as the result of a swollen lymph node, a condition called axillary lymphadenopathy. Lymph nodes exist under your armpit and other places throughout your body. They swell while producing immune cells to help fight infections and other foreign substances.

A swollen lymph node under your arm feels like an armpit lump when you massage or press down on your arm. The most common reason that a lymph node swells is in reaction to a bacterial, viral, or fungal infection near your arm or elsewhere in your body.

In addition to an infection, the following factors can also make a lymph node swell:

An armpit lump can also occur due to causes unrelated to a swollen lymph node. These factors can include the following conditions:

  • Cyst
  • Lipoma (soft, fatty growth)
  • Mastitis
  • Certain vaccinations, including the COVID-19 vaccine

When to Seek Emergency Care

An armpit lump accompanied by signs of infection requires emergency care. Without treatment, you can risk the lump forming an abscess and causing a serious illness like sepsis. Seek immediate care if you have an armpit lump with any of the following symptoms of infection:

Is an Armpit Lump a Symptom of Breast Cancer?

While an armpit lump can be a symptom of breast cancer, it is relatively rare for an armpit lump to be the initial sign of breast cancer. Instead, most breast cancers appear as a mass or abnormality on the breast.

To determine whether your armpit lump is linked to breast cancer, you must consult with a healthcare provider for a physical examination.

When an armpit lump occurs, there are a few reasons that it can be a symptom of breast cancer. These factors include:

  • Breast cancer has spread to the lymph nodes in the armpit: A tumor that starts in breast tissue may shed breast cancer cells. Breast tumors usually drain toward the underarm. Since the axillary (underarm) lymph nodes are so close to the breast, the cancer cells usually reach these lymph nodes before they reach others in more distant parts of the body. As the lymph nodes release immune cells to fight the breast cancer cells, they swell. Breast cancer is regarded as lymph node-positive when breast cancer cells exist in the lymph nodes. The accumulation of breast cancer cells and waste can build up and form a lump.
  • A tumor has formed on accessory breast tissue: Accessory, or residual, breast tissue in the armpit area occurs in about 6% of the population. It can resemble an extra breast or may be unnoticeable to those who have it. However, since it is breast tissue, it remains susceptible to breast cancer, mastitis (painful infection), and other conditions that affect all breast tissue.
  • A tumor has formed on the axillary tail of Spence: While the area commonly described as your breast sits on top of your chest muscle, breast tissue extends from the edge of your sternum to the center of your underarm. The term "axillary tail of Spence" describes a narrow portion of the mammary gland that extends to the underarm area. This area contains breast tissue and lymph nodes. This makes it vulnerable to the formation of a tumor from breast cancer cells, even though it isn't part of the area commonly considered the breast.

Treatment of an Armpit Lump

The treatment you receive for an armpit lump depends on its cause. Some armpit lumps will go away on their own without treatment. An armpit lump caused by an allergic reaction will likely clear up when the allergen is removed. If the armpit lump is linked to an infection, it may go away with a course of antibiotics. Some types of lumps may require surgical removal.

If cancer is suspected, your healthcare provider will want to confirm the diagnosis. Treatment of the lump is based on a detailed medical history, including the duration of the lump, the condition of the lump, and your history of breast cancer or any other cancer.

Your healthcare provider will likely request certain medical tests to confirm your diagnosis. These tests can include:

If cancer is detected, treatment may include:

When to See Your Healthcare Provider

While an armpit lump can occur from a relatively harmless reaction to antiperspirant, you won't be able to determine this on your own. It's not possible to diagnose the cause of an armpit lump by touch or appearance. You have to consult with a healthcare provider to get an accurate diagnosis.

You may notice an armpit lump because it is annoying. It can also feel like a raised pea during a breast self-exam (BSE). It is usually safe to wait a few days to see how it progresses. If the armpit lump occurs as a reaction to inflammation or another harmless cause, it may disappear on its own without treatment.

If your armpit lump worsens or doesn't improve over time, it should be examined by a healthcare provider. You should also seek medical attention if your armpit lump has any of the following symptoms:

  • A rock-hard feeling
  • A marble shape
  • Redness, pain, fever, or other signs of infection
  • Pus or another liquid oozing from the lump
  • Pain or discomfort that interferes with daily life


An armpit lump, or axillary lump, can occur as a symptom of breast cancer but is more likely to happen as the result of an enlarged lymph node or other problem. In many cases, an armpit lump occurs as the result of an infection, cyst, skin problem, or an allergy to body care products.

There is no way to know whether an armpit lump is linked to breast cancer by feeling it. An armpit lump that is hard and doesn't change should be checked by a healthcare provider. They can find the source of the problem and advise you on the right treatment.

A Word From Verywell

It can be frightening to notice an armpit lump. While it's likely a harmless bump, it's normal to worry that the lump might be a sign of breast cancer. Getting an early and accurate diagnosis of the lump is the best way to ease your concerns and get the treatment you need. This is especially important if the lump proves to be malignant.

Dealing with breast cancer can be an overwhelming experience. You may benefit from speaking to others who have gone through the same experience. Consider joining an online or in-person support group for people who have metastatic breast cancer. With the right support and treatment, you can achieve optimal results.

Frequently Asked Questions

  • When is breastfeeding the cause of an armpit lump?

    While most of your breast sits on top of your chest muscle, some breast tissue extends from the edge of your sternum out to the underarm. Lumps can occur when there is a buildup of breast milk due to a blocked duct or engorgement in the mammary glands under your arm.

  • Does a cancer lump in the armpit feel different from other armpit lumps

    While it is impossible to determine the status of an armpit lump by touch, there are some characteristics that are more common with a cancerous armpit lump. A cancerous lump is often rock hard and similar to the shape of a marble. It usually doesn't have external signs of infection. The only way to know the source of your armpit lump is to contact your healthcare provider for an examination and diagnostic testing.

  • What is hidradenitis suppurativa?

    Hidradenitis suppurativa, also known as acne inversa, is a chronic, noncontagious skin condition that causes lumps deep under your skin. The lumps usually develop in areas where two areas of skin naturally rub against each other, like the armpits or inner thighs. The lumps can be painful and leak fluid. Without treatment, nonhealing wounds can result.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Anna Giorgi
Anna Zernone Giorgi is a writer who specializes in health and lifestyle topics. Her experience includes over 25 years of writing on health and wellness-related subjects for consumers and medical professionals, in addition to holding positions in healthcare communications.