Breast pain is often not a sign of breast cancer. But some women may have breast pain and have breast cancer. According to the American Cancer Society, a new breast lump or mass is often the most common sign of breast cancer. But most breast lumps are benign, and not cancerous. You are more likely to have cancer if your breast lump or mass has irregular edges. Often these lumps are painless or hard. But some breast cancers can form soft, round, tender or even painful lumps or breast changes.