Some common signs that may suggest cancer include unexplained weight loss, persistent tiredness, unusual lumps or swellings, changes in the skin such as new moles or sores that do not heal, persistent pain, or changes in bowel or bladder habits. Other warning signs may include persistent coughing, difficulty swallowing, or unusual bleeding. These symptoms do not always mean cancer, but if they last more than a few weeks, it is important to see a doctor for evaluation.