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.

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:

• Inflammation due to injury
• Immune and autoimmune disorders
• Breast cancer or other cancers such as leukemia, Hodgkin's lymphoma, or non-Hodgkin's lymphoma
• Allergic reaction to certain medications or body care products

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

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:

• Complete blood count (CBC)
• Fine-needle aspiration to examine fluid from the lump
• Mammogram
• X-ray
• Magnetic resonance imaging (MRI)
• Computed tomography (CT)
• Biopsy of the tumor or affected lymph node (removal for analysis in a lab)

If cancer is detected, treatment may include:

• Chemotherapy
• Radiation therapy
• Hormone therapy
• Cancer-treating drugs
• Surgical removal of the tumor
• Surgical removal of some or all the lymph nodes in axillary lymph node dissection
  

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
  

Summary

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.