- Most of the time, a lump under the armpit is an enlarged lymph node.
- In rare circumstances, an enlarged lymph node that has certain characteristics can be a sign of cancer.
- Regardless of the features of the lump or the symptoms accompanying it, if it does not resolve on its own, it is reasonable and likely a good idea to have it check out by a doctor.
Finding an unusual lump in your armpit can be alarming — but most of the time, a lump under the armpit is not something to be overly concerned about.
Adrienne Waks, MD, a physician in the Susan F. Smith Center for Women’s Cancers at Dana-Farber, answers some of the most commonly asked questions about a lump under the armpit, including when you need to see a doctor.
What does a lump under the armpit mean?
Most of the time, a lump under the armpit is an enlarged lymph node. Lymph nodes are an important part of the immune system and can swell when the body is fighting off an infection or dealing with an injury.
If the skin looks normal, but there is a bump that can be felt under the skin, the lump may be an enlarged lymph node.
It is usually advised to monitor the lump for a few days to see what happens. If the lump goes away, then the lymph node most likely became swollen in response to an infection or inflammation. Symptoms such as redness, pain, or fever accompanying the swollen lymph node can be symptoms of infection that should be checked out by a doctor.
Another common explanation for a lump under the armpit is something in the skin, such as a cyst or a blocked hair follicle.
In rare circumstances, an enlarged lymph node that has certain characteristics can be a sign of cancer.
What does a cancer lump in the armpit feel like?
A normal lymph node should have the shape of a lima bean. It should also be somewhat firm, but still have some give to it. A cancerous lymph node will often become rock hard. It will also lose the lima bean shape and become more rounded like a marble.
If a swollen lymph node is overly firm and is not shaped like a lima bean, it could potentially be cancerous. Likewise, if the lump is obviously not in the skin, and if it persists, gets larger, and is not accompanied by signs of an infection, it may be time to seek medical attention.
Remember: It is impossible to diagnose cancer by touch — so if you are concerned or notice these symptoms, you should contact your doctor. While a lump in the armpit is usually not something to worry about, and the explanation for it is usually something mild and relatively harmless, it is better to be safe and have it checked out.
A painful lump in the armpit
A painful lump in the armpit can potentially be cancerous, but usually when a lump is painful or tender, there is another cause. Infection or inflammation tend to cause pain and tenderness, whereas cancer is less likely to be painful. A lump in the armpit tends to be more concerning if it is painless.
Regardless of the features of the lump or the symptoms accompanying it, if it does not resolve on its own, it is reasonable and likely a good idea to have it check out by a doctor.
About the Medical Reviewer
Dr. Waks received her undergraduate degree from Princeton University in 2006 and her MD degree from Harvard Medical School in 2011. She completed residency training in internal medicine at Brigham and Women's Hospital, where she subsequently served an additional year as a Chief Resident in Internal Medicine. She completed fellowship training in medical oncology at Dana-Farber/Partners CancerCare, then joined the staff of the Breast Oncology Center at Dana-Farber Cancer Institute.