Mucinous Adenocarcinoma of the Colon and Rectum


Colorectal cancer is a term used to describe a wide range of cancerous malignancies affecting the colon and rectum.

Of these various types, there is one that stands out as the primary form affecting more than 125,000 Americans each year. It is called adenocarcinoma and accounts for 95 percent of all colorectal cancers in the U.S. In addition to classic adenocarcinoma, there two less common subtypes, known as:

Of these subtypes, MAC is more frequently seen and accounts for between 10 and 15 percent of all colorectal cancers.


Understanding Adenocarcinoma

Adenocarcinoma refers specifically to cancers that affect cells that are glandular in nature. “Adeno-” is the prefix for “gland,” while “-carcinoma” is a term used to describe cancers that begin in the skin or in tissues that line the organs.

Adenocarcinomas develop because the colon is made up of a vast network of glands, which serve two key functions:

  • to absorb water from the feces back into the blood
  • to secrete mucus into the colon to lubricate feces as they are expelled from the body

If these cells are unable to produce ample mucus, the lining of the colon can become damaged as unlubricated stools abrade and damage them. Over time, this can lead to damage on the genetic level, causing the cells to multiply abnormally without any means to prevent or temper replication. It is this factor that triggers the formation of adenocarcinoma.

How Mucinous Adenocarcinoma Differs

Though they may have originated from the same genetic cause, MAC differs from adenocarcinoma in that, instead of producing less mucus, the colon produces far more.

MAC is characterized by the formation of a tumor comprised of at least 50 percent mucin.  Mucin is not mucus per se, but rather the glycoprotein component of mucus and other bodily fluids (such as saliva and breast milk). It is this mucinous component that many believe helps a tumor spread more aggressively as it seeps beyond the walls of the tumor to the adjacent tissue.

As such, MAC has long been considered a more aggressive form of adenocarcinoma and to be far less receptive to treatment. Both of these beliefs are still hotly debated among researchers, some of whom hypothesize that it is not the speed of development but rather the stage when the tumor is found that leads to poorer outcomes.

There is certainly evidence to support this. Generally speaking, MAC is diagnosed in the more advanced stages of the disease. This is due, in part, to the fact that mucinous tumors have a far softer consistency than “standard” tumors and are often not detected until they are larger and more pronounced.

Even when detected early, the tumor’s poorly defined shape and border make it hard for even experienced pathologists to properly stage.

On the other hand, MAC has an entirely different molecular “signature” from adenocarcinoma. While we don’t yet know how this relates to disease progression—it may or may not—we do know that mucinous cancer tends to be less genetically stable (a state we refer to as microsatellite instability) than non-mucinous cancer.

These aberrations are largely responsible for triggering the excess production of mucin. The mucin, in turn, creates a barrier that may, in fact, prevent chemotherapy medications from effectively penetrating cancer cells. In short, the chemo may not be able to get where it needs to be.

A Word From Get Meds Info

While it’s clear MAC has distinct characteristics that make it harder to diagnose (and may lead to shorter survival times), there are factors we know are closely associated with its development:

If you have any early signs of colorectal cancer and you have a family history of the disease, it’s important to take extra steps if early investigations are inconclusive. MAC is often easy to miss during a biopsy and may be more easily spotted using magnetic resonance imaging.

Do not hesitate to request further investigation if symptoms persist or worsen. Alternately, you can seek a second opinion from a colorectal specialist experienced in MAC and signet-ring cell carcinoma.

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