Can a lymph node under the opposite armpit be swollen in cases of breast cancer?

It’s very much unlikely. If the opposite armpit develops swollen nodes, it could be anything from an ingrown hair to a skin disease, to a swollen lymph node caused by an infection or even an injury down your arm. Many of these conditions require further testing or treatment. It is important to see your physician if you are experiencing this.

Lymph nodes, small structures that house immune system cells called lymphocytes, are found in the breasts and shoulder, under the arm and throughout the body. Breast cancer cells can begin to colonize lymph nodes, leading to an enlargement and matting of the nodes. If breast cancer spreads to lymph nodes in the shoulder, patients may notice a lump under the arm corresponding to clusters of enlarged lymph nodes.

Over time, cancer cells in the lymph nodes can enter the lymph vessels and metastasize, colonizing tissues in the shoulder or other distant tissues throughout the body.

Although other medical conditions, such as infections, can lead to swollen lymph nodes, unexplained lumps in the armpit or shoulder should be examined for the presence of cancer.