Cancer pain can be acute or chronic and is caused either by the disease itself, or as a result of the treatment. For example, acute pain might be caused by surgery to remove a tumor. Chronic pain might be caused by the spread of the disease to other parts of the body.
Cancer is the abnormal growth of cells in the body that leads to the formation of a tumor. Not all tumors are cancerous. Benign tumors are non-cancerous, as they do not attack healthy tissue or spread to other parts of the body. Malignant tumors are cancerous, resulting from the uncontrolled growth of cells that have been changed by some type of genetic change (mutation) or damage. Due to the damage or mutation, these cells lose the message that tells them to stop growing. They invade and destroy healthy tissue.
Malignant cells can also break away from the original (primary) tumor and spread through the blood or lymphatic system to form a new tumor in another part of the body. The spread of cancer to other parts of the body is called metastasis. Cancers that have metastasized are more likely to cause pain, as this represents a more advanced disease.

Signs and Symptoms of Cancer Pain
There are three main types of pain seen in cancer: somatic, visceral and neuropathic cancer pain. Somatic pain is pain felt by the pain receptors of the body and is often described as aching, dull, sharp, or throbbing. Examples are pain in an incision after surgery, or from a cancer that has spread to the bones.
Visceral pain is caused by tissues or organs in the abdomen that are being stretched or enlarged by cancer. The pain is commonly described as deep, squeezing or as a feeling of pressure. The pain might also be referred to other areas. For example, pain from gallbladder disease is often felt in the right shoulder.
Neuropathic pain is caused when nerves are damaged by cancer or cancer treatments. This pain is usually described as burning, shooting or stabbing.