Understanding colon cancer: a tour of your innards


At 2 a.m., the floor trembled and the walls rattled. It happened every night at the Kahler.

Bowel preps hit 50 intestinal tracts. Toilets flushed en masse. That joke about the venerable hotel across the street from the Mayo Clinic was repeated for years.

Black humor about the unhappy need to cleanse bowels before colonoscopy helped make the experience more tolerable. I want you to play along with me. You’ll perform an inspection of a clean, pink intestine.

Should lumps and bumps all be removed? What are risks and benefits? Nothing in life comes without some of each. The philosophical me breaks through at times. Mea culpa.

A primer: Carcinoma is a kind of cancer that occurs in tubular structures. Carcinogens we breathe endanger our airways. The lining cells of the intestinal tract, from mouth to anal verge are exposed to direct contact with things that we eat, including products that result from interactions between food and the digestive process.

We can start with the idea that these chemicals damage DNA. Naturally that is part of the story, but incomplete. DNA begins to make weird proteins and to allow growth when normal biology would shut it down. That’s badly oversimplified, but a starting point.

Your patient is on the table, doctor, sleeping comfortably and squeaky clean inside. Pick up the scope and let’s take a look.

The patient is anemic. In men, stomach and duodenal ulcers are a common cause.

In women we’d think about uterine bleeding. You suspect blood loss from somewhere farther down the line, the lower intestine. Sources may be seen around the anus or low rectum, the home of hemorrhoids.

These are benign swellings of veins that usually bleed bright blood and sometimes hurt. You see nothing there. Move the scope around to the appendix. Work around the curves of the sigmoid, up the left side, and across to the patient’s right.

You encounter no blockages or sources of bleeding, until you direct the lighted end at a growth on a curve near the liver. It looks like a morel mushroom. It sits on a stalk and it’s a half-inch across.

Should you snip it off? Why? What’s the chance that it could become a cancer? What are the chances that you’ll poke a hole through the bowel wall or cause an infection? What are the chances that you’ll be sued for the choice you make? If anyone tells you that they have perfect answers, they’ve been reading only studies that support their point of view.

We’re pretending that you are the doctor. You’re going to be sitting with your patient, trying to be supportive and honest at the same time, but the issues are sticky. There is no single definition of cancer, much less “early” cancer. Those terms have been used loosely. The role of genetics and other causes of cancer are often misrepresented. It’s hard to find the truth, but the future is looking better.

While you look at that tiny mushroom, I whisper, “Snip it off, because that’s what is usually done, and we can defend the decision if we’re challenged.”

I don’t add that you get paid for removing it and if it happens to be a missed malignancy, you’re in trouble. I believe that most physicians act in accordance with their patient’s best interest and in accordance with their interpretation of the literature, but this article isn’t about what I believe, so let’s leave your imaginary patient sleeping on the table and follow the polyp to the pathologist. Let’s consider the facts.

When the pathologist makes slices through the polyp you removed, she’ll look for cell shape and organization, active growth patterns and invasion.

Normal cells originate on the DNA template. They are similar to each other in size and shape. Many polyps are benign and show an increase in the total number of cells — hyperplasia — in which things maintain their original structures.

Signs of cancer can include variations in the appearance of the cell and its nucleus, increased division — mitosis — and invasion into adjacent normal cells or into lymph channels or blood vessels.

More abnormal findings mean a more likely risk that the lesion is cancer.

Be aware that pathologists generally agree, but not always. Also understand that the shape of cell gives us clues to malignancy, but we are still learning about the DNA changes that are more important determinants of the outcome.

It’s interesting that the pathologist needs more than one feature to judge malignancy, and we might expect that she will also mention that polyps like this are more common on the left side of the colon. The location worries her a bit. Tumors on the right have a slightly different outlook and patterns change with age.

The data supporting colonoscopy is strong, if imperfect. Science, devoid of ethics, would suggest leaving polyps to see what happens. Since we take them out, we have to resort to less reliable data sets, but we can say for sure that patients in high quality screening have a 53 percent lower risk of dying from a colon cancer.

Using CT scans instead of colonoscopy is being studied and may add to our understanding. The risk of complications requiring hospitalizations was 1/200 biopsies in one major study. The dollar cost per life saved is high, but probably a bargain compared with breast or prostate screening.

My subsequent reports will look at the science linking polyps to cancer and challenging whether dietary risk reduction is anything more than gaseous hyperbole.

Dr. Larry Mulkerin is a retired clinical professor. He can be reached at mulkerin@charter.net.


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