MECHANISM OF CANCER PAIN

The most common mechanism of cancer pain is associated with tumor invasion and subsequent tissue damage that activate pain receptors. Therapy can also be associated with pain induction. For example, although surgery and radiation therapy can relieve pain and suffering, they can also cause significant discomfort due to tissue and nerve damage. Alkaloids such as vincristine and vinblastine can produce polyneuropathy, which has been noted to be painful in human cancer patients.

The types of cancer pain include visceral pain, inflammatory and somatic pain, neuritis, and neuropathic pain.

Visceral Pain

Visceral pain is a dull, deep, constantly aching pain. It is also poorly defined and often responds best in human patients to narcotic analgesics when pain is significant. Whether fentanyl is helpful in these cases is unknown; however, ileus is a possible complication of fentanyl use.

Inflammatory and Somatic Pain

Inflammatory and somatic pain is frequently described as well localized, constant, and aching. Common sources of this type of pain include bone metastases, tissue damage, and musculoskeletal, dental, and integument pain. In humans, this type of discomfort responds well to analgesics such as aspirin, acetaminophen, or the nonsteroidal anti-inflammatory drugs (NSAIDs). Fentanyl patches may be of value.

Neuritic Pain

Inflammation of nerves or nerve roots, which can be a paraneoplastic syndrome or a direct effect of cancer compression, causes neuritic pain. Humans describe this as a constant dull aching pain that may have periods of burning "shock-like" sensations.

Neuropathic Pain

Neuropathic pain is the result of a damaged segment of the nervous system that normally transmits pain stimuli. This is due to metabolic, immunologic, or direct physical effects on the nervous system. It is difficult to control with standard analgesics. Fentanyl is no exception.