Cancer pain and symptoms of cancer pain are a concern for many people who suffer from skin cancer. Pain expert Dr. Scott Fishman answers questions about cancer pain and symptoms of cancer pain:

Q:  How come some people don't feel cancer pain until it is too late?

A:  Pain travels along nerve pathways (think of them as highways) with some pain signals traveling much faster than others. Some cancers cause sudden onset of pain at the earliest and most treatable time in the disease course, while others become painful long after effective treatment no is longer possible.

For instance, pancreatic cancer is one of the most virulent and painful tumors and can sneak up on a person with deadly force. The pain may begin as an innocuous backache that won't go away and may defy a host of diagnoses and treatments. This pain is so deceptive because its symptoms erupt long after the disease has burrowed into the body and become entrenched. Months may pass between the onset of the pain, which may feel like achiness that shifts between the ribs and back, and a scan of the abdomen detects a spot on the pancreas.

Pain spreads out from a damage site and moves along many nerve pathways, each carrying distinctive pieces of information and operating at different speeds. While low-threshold nerve pathways constantly register fine tactile sensation, higher threshold pathways are reserved for pain sensation. (It is clearly not in the body's interest to have a hair-trigger pain threshold.)

Certain pathways specialize in sharp, pointed feelings and transmit stinging pain very quickly — so fast in fact that it feels instantaneous. Other nerves move information along much more slowly and transmit dull, aching, or burning pain.

So when you cut your finger with a knife, you first feel the sharp sting and only later feel the aching or uncomfortable burning feeling. A common example of a slow-moving pain signal is the sting of sunburn, which comes hours after the initial tissue damage.

Nerves are the highways along which the pain signals travel. The pain sensation makes a number of stops in route to the brain, and then circulates to various regions of the brain, like the thalamus and hypothalamus. Depending on which part of the brain the pain arrives at first, the message may evoke a verbal "Ouch!" or it may be forwarded to motor nerves that command a physical flinch, or both.

As sensory signals hustle along nerve routes carrying messages back and forth between injured tissue and the brain, other nerves are relaying information about the damage and instigating a response.

Along the way, pain stimulates a chain reaction of neurochemicals that either intensify or dampen the sensation. Neurochemicals bearing messages about the pain speed to various parts of the body and brain and account for a host of reactions, including swelling, inflammation, itching, muscle spasm, accelerated heart rate, and even sweating.

Your internal structures, as well as your skin, are laced with pain sensors. Just as some areas of your skin are more sensitive to pain than others, so too are your innards. Your muscles possess the richest supply of internal sensory nerves. They are followed in declining order of sensitivity by the tendons, joints, ligaments, and the outer layer of bones.

The hierarchy of pain nerve distribution explains why muscle aches are so common and why musculoskeletal pain is what often propels people to consult a doctor. This hierarchy also explains why bone pain caused by cancer is felt long after the disease has invaded the body.