Common Worry: Trauma Causes Breast Cancer If you’ve bumped, bruised, or injured your breast and felt a wave of fear afterward, you’re not alone. So many people worry that an old injury is the reason behind a diagnosis. That worry is real and valid, and it deserves a clear, honest answer. Here’s the truth: an injury to your breast does not cause breast cancer. Sometimes an injury brings you in to get checked, and a lump gets found around the same time. That timing can make it feel connected. But