An armpit lump—or axillary lump—can occur as a symptom ... It is uncommon for females under age 40 to develop breast cancer. For females in their 30s, the risk of developing breast cancer ...

Cysts (fluid-filled tissue pockets), infections, and swollen lymph nodes commonly cause armpit lumps. Finding a lump in your armpit can be worrisome, especially if it hurts or appears unexpectedly.