A new lump or swelling in the neck, armpit, or groin could be a sign of an infection or inflammation, but it could also be a sign of abnormal cell growth. It could be a sign of something more serious, like breast, testicular, or lymph-related cancers, if it feels hard, gets bigger over time, or doesn’t go away. To figure out what’s wrong, you need to keep an eye on its size, shape, and tenderness.