| The Nature of Cancer | |
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by Laura Dolson
Note that the descriptions below do not fit for all cancers, but they are true for most solid tumors. Leukemia would be one large exception - it isn't a "tumor" in the sense we usually think of them.
The Beginning
What starts a normal cell on the path to cancer? Scientists are constantly trying to improve their knowledge about this. We know some things, for example, radiation (including the Sun's radiation) can bring about cancer-causing mutations in cells. We know some predisposing factors - genetics, certain chemicals, viruses like HPV - but the exact mechanisms in most cases are still being clarified. In any case, cancer begins when a normal cell is influenced to change its genetic code - its DNA - in a way that causes it to "go off on its own". Thereafter, all the cells that descend from that cell have the altered DNA, and form an abnormal "colony" of tissue.
Over time, this colony actually takes on some of the characteristics of its own separate body organ. Far from being just a blob of cells, the tumor acquires "parts", roughly divided into the "stroma" and the "parenchyma". These are the same tissue types that make up most organs in the human body. The stroma is the part of the organ that can be thought of as its supporting structure, and includes connective tissue, blood supply, and lymphatic vessels. The parenchyma is the part of the organ that carries on the biochemical "work" of the organ, be it liver, stomach, or spleen. In the case of a tumor, the work of the "organ" is making more "neoplastic" (cancerous) cells, and invading surrounding tissues. It also continues to carry on some of the functions of the parent organ, and the cells, though altered, are still identifiably from that organ.
How do malignant tumors differ from normal tissue? Here are the basic ways in which cancerous cells and tumors differ from their normal counterparts. As we will see in the section "How Cancer Treatments Work", some of these very characteristics cause cancer cells to be more vulnerable to treatments.
1) They are growing faster than they are dying off, and are less subject to the controls of normal cells. There are several places in the cell cycle where this can occur; basically they can multiply faster, age more slowly, and/or not die off as quickly. Although it is very common to say so, it's not technically factual to say that cancers grow in an "uncontrolled" way. Many tumors grow more slowly than some other normal tissues. No tumor grows nearly as fast as an embryo or the lining of the intestine, for example. (The intestinal lining grows quickly and also is sloughed off at a rapid rate.)
2) They invade normal tissue, eventually compromising the function of the organ in which they begin. This may happen very slowly or more quickly, depending on the aggressiveness of the tumor.
3) They metastasize - cells travel through blood, lymph, or body cavities to remote locations in the body. The vast majority of these cells die, but some may begin multiplying to form a new tumor. Wherever the metastasis is, it retains the characteristics of the original tumor - for example, uterine cancer would stay uterine cancer even if it spreads elsewhere.
4) They are genetically abnormal and unstable. The cells tend to have large nuclei with extra chromosomes, and produce more mutations over time.
5) Tumors are less well-organized than the organs in which they arise. The architecture of a tumor is much less specialized, and the cells don't work as well together as that of a normal organ. Also, they contribute nothing to the functioning of the body as normal organs do.
What about benign tumors?
Benign tumors, such as uterine fibroids, grow faster than the surrounding tissue, at least at first. At some point, they may or may not stop growing faster than they are dying off. Although they may grow big enough to cause problems by pressing on other structures, they do not invade that tissue, and they don't metastasize. We will learn more about benign tumors in the "Tumor Types" section.
Next page > Tumor Types > Page 1, 2, 3
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Copyright © 2001 by Laura Dolson. All rights reserved. Please submit reprint requests to gyncancer@baymoon.com
The material on this page and Web site is for informational and educational purposes only, and should not substitute for medical advice. Anyone having questions about the application of information appearing here to a specific person or situation should obtain advice from a qualified physician.