Mastalgia: Pain in the breast or mammary gland, whether serious or not. Mastalgia has many causes including injury, infection, and plugged milk ducts. QUESTION A lump in the breast is almost always cancer. See Answer From Cancer Resources Cancer Treatment TypesWhen Cancer Spreads Beyond Your BreastEarly-Stage Breast Cancer Treatment Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19