Could a swollen lymph node be breast cancer?

Possibly: A swollen lymph node in the armpit could be from breast cancer but in most patients, it is much more likely to be a benign swelling from a number of other causes. Regardless, you should have your doctor check it out.

Could be many things: Swollen lymph node in the arm pit can be caused by various things like reactive process to infection, trauma, inflammation, etc- including malignancy- could be breast, lymphoma etc. Infection is the most common thing that give you swollen lymph node. To be sure, however, go to see your doc and have yourself checked carefully. Good luck.