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Causes of cancer pain


Cancer pain can be caused by pressure on, or chemical stimulation of, specialised pain-signalling nerve endings called nociceptors (nociceptive pain), or by damage or illness affecting nerve fibers themselves (neuropathic pain).

Infection of a tumor or its surrounding tissue can cause rapidly escalating pain, but is sometimes overlooked as a possible cause. One study found that infection was the cause of pain in four percent of nearly 300 cancer patients referred for pain relief. Another report described seven patients, whose previously well-controlled pain escalated significantly over several days. Antibiotic treatment produced pain relief in all patients within three days.

Tumors can cause pain by crushing or infiltrating tissue, or by releasing chemicals that make nociceptors responsive to stimuli that are normally non-painful (cf. allodynia).

Between 40 and 80 percent of patients with cancer pain experience neuropathic pain.

Brain

Meninges

Spinal cord compression

Nerve infiltration or compression

Dorsal root ganglion inflammation

Brachial plexopathy

Invasion of bone by cancer is the most common source of cancer pain. About 70 percent of breast and prostate cancer patients, and 40 percent of those with lung, kidney and thyroid cancers develop bone metastases. It is commonly felt as tenderness, with constant background pain and instances of spontaneous or movement-related exacerbation, and is frequently described as severe. Tumors in the marrow instigate a vigorous immune response which enhances pain sensitivity, and they release chemicals that stimulate nociceptors. As they grow, tumors compress, consume, infiltrate or cut off blood supply to body tissues, which can cause pain.

Fracture

Skull

Pain produced by cancer within the pelvis varies depending on the affected tissue, but it frequently radiates diffusely to the upper thigh, and may refer to the lumbar region. Lumbosacral plexopathy is often caused by recurrence of cancer in the presacral space, and may refer to the external genitalia or perineum. Local recurrence of cancer attached to the side of the pelvic wall may cause pain in one of the iliac fossae. Pain on walking that confines the patient to bed indicates possible cancer adherence to or invasion of the iliacus muscle. Pain in the hypogastrium (between the navel and pubic bone) is often found in cancers of the uterus and bladder, and sometimes in colorectal cancer especially if infiltrating or attached to either uterus or bladder.


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