Losing weight without trying is a common sign of cancer. When the above signs and symptoms are accompanied by unexplained weight loss, fatigue, or weakness, it could indicate breast cancer. If you have a family history of breast cancer, genetic mutations like BRCA2, or conditions like Klinefelter syndrome, it is important not to dismiss the signs. Also, know that these symptoms can happen with other conditions that are not cancer. If you notice any of these symptoms or changes, consult your doctor right away.