Survivor since 2007
If you are asking about breast cancer specifically, you won't feel sick unless it has metastasized (spread) to an organ, bones, brain, etc. Some women, have symptoms with breast cancer like itching, pain, tingling, inverted nipple, discharge from the nipple, some type of sensation in the breast that is out of the ordinary. Some women have no discomfort or sensation from breast cancer. Once breast cancer has metastasized to an organ, a person may then develop different symptoms that would make them "feel sick." Breast cancer is sneaky! The best outcomes happen when the disease is caught early and treated successfully.