Unexplained weight loss why does it happen to people with undiagnosed cancer

One major reason for weight loss with undiagnosed cancer is called tumor induced weight-loss or cancer cachexia. This is when a tumor made up of cancer cells use energy and change how calories are stored and burned. Basically the tumor uses energy and burns more calories. This results in loss of appetite, which also contributes to the loss of weight as now there is even less for the cell to use.