Oncology 101: The Basics of Cancer

by Kelly Erickson, MD | erickson@myhousecallmd.com

We all know what “cancer” is, but when you or a loved one hears it as a diagnosis in the physician’s office, the word suddenly takes on a whole new meaning.  Not only may you become overwhelmed with emotions and the notion of mortality, but also with an entirely new vocabulary.  The number of words the medical community has conjured up to describe cancer is astounding.  As scary as it sounds, your understanding of cancer and the terms we use to describe it are paramount to your personal decisions and treatment.  Here we will explain the basics of cancer as well as outline some of the most commonly used terminology in the field of oncology (a.k.a. cancer…and the vocabulary lesson begins).

What is cancer?

Cancer is the result of mistakes or uncorrected errors (a.k.a. mutations) in the DNA of your own cells.  Your DNA serves as both the blueprint and command center for each individual cell in your body, instructing it via complex biochemical pathways that communicate which actions the cell should take, how it should move and what types of substances to produce (think hormone excretion, saliva production, or bone deposition).  Every cell has a particular role it fulfils to keep things running smoothly in the microcosm of your body.

Cancer results when an error occurs in the portion of your DNA responsible for cell growth. When this occurs, the command center constantly tells the cell to grow and reproduce without any regard for the external signals your body may be sending telling the cell to stop.  The problem gets even hairier because most cancer cells lack the ability to correct errors that arise in their genome.  Therefore, mistakes that would normally be checked and corrected are now passed on to all of the tumor cell replicates…creating a growing army of out of control cells.  Similar to the double agent in the action movie who turns out to be working for the bad guys, cancer is the result of your own cells turning against your body as they respond to an incorrect signal to grow.  Another key point about cancer cells is that they are almost identical to our own cells, making them not only difficult to identify, but also extremely difficult to kill (similar to the rogue agent).  Thus, the difficulty in finding the “cure” to cancer stems from this inherent predicament.

Where did the cancer come from?

This question is much more difficult to answer.  Simply stated, cancer is caused by mutations in your DNA, the command center of the cell.  While we have identified common patterns in the types of mutations that occur in cancer cells and have discovered many locations where DNA is most susceptible to mistakes, errors or damage, many cancers arise from unique mutations in a DNA sequence that are difficult to locate.  As previously explained, since many cancer cells lose their ability to repair mistakes in DNA as they arise, cancer cells tend to accumulate multiple mutations over time, further complicating the problem.

Some of the most common culprits of DNA damage include:

  • Chemical carcinogens (a.k.a. “cancer-causers” such as tobacco smoke, alcohol, and asbestos) are thought to cause cancer by inducing mutations, damaging cells and increasing the rate of replication, making cells more susceptible to errors as the DNA replicates.
  • Radiation, which can come from a variety of sources including radioactive compounds (most people think Chernobyl, but for most of us the likely exposure here is CT scans or therapeutic radiation which will be discussed later).
  • Infections, most commonly viruses, have been shown to cause certain types of cancer.  One of the more well-known viruses is the Human Papilloma Virus (HPV), which causes cervical cancer.  Hepatitis B and C viruses are known to cause hepatocellular carcinoma (liver cancer) and Epstein-Barr virus causes nasopharyngeal cancer and certain types of lymphoma.
  • Heredity (a.k.a. what is passed down via our genes and is notably out of our control) is also responsible for increasing the chances of an individual being diagnosed with cancer.  There are many rare and serious conditions that are associated with high rates of cancer (for example Multiple Endocrine Neoplasia, Li Fraumeni and Turcot Syndrome).  These patients commonly possess a hereditary genetic mutation that makes them more susceptible to specific types of errors in their DNA and subsequently more likely to develop cancer.  The well known “breast cancer genes,” BRCA-1 and BRCA-2, are more common and are typically found in patients who are otherwise healthy but have a higher risk of developing breast cancer at some point in their lives as a result of these genes.  There are likely hundreds of other cancer susceptibility genes to be discovered that, if present, increase a patients’ chance of developing a specific type of cancer.  In the future, we expect testing for these genes to become more prevalent and also increasingly controversial.

Is cancer more prevalent today than it was 100 years ago?

It is hard to know the true answer to this question but the most widely accepted answer to this question is actually, “No.”  What has increased is the numbers of people diagnosed with cancer, not the number of people who actually have cancer.  The increase in the number of people diagnosed with cancer it the result of our diagnostic methods, methods that have improved dramatically from 100 years ago.  We are simply getting better at recognizing and diagnosing cancer, leading to an increase in the number of people who know they have cancer without increasing the total number of people with cancer.  The other consideration is that, as our population ages and the average life expectancy increases, the likelihood of developing cancer increases.  As we already explained, the “mistakes” that occur in a patient’s DNA that lead to cancer are more likely to occur in older cells.  It makes sense that older people are more likely to get cancer than younger people.  The older the population become, the more cancer we expect to see.

Do water bottles cause cancer cause cancer?  What about cell phones?

The water bottle myth received an incredible amount of attention…and is completely false.  For those of you living under a rock for the last few years, there have been many rumors alleging that heating or even freezing plastic water bottles releases chemicals into the water and that those chemicals cause cancer.  This myth was based on a hoax email entitled “Johns Hopkins Cancer Update” that spread like wildfire.  The e-mail has since been debunked by Johns Hopkins University and the American Cancer Society, both confirming that the rumor is false.  The email claimed that plastic water bottles contained chemicals, called dioxins, that are released into the water when the bottles are heated or frozen.  The truth is that plastic water bottles do not contain the potentially harmful dioxins.  While we have not conducted studies in humans (imagine trying to sign people up for that study), animal studies give us no reason to believe that cancer-causing chemicals are released from water bottles.

Concern over the widespread use of cell phones and the possibility that cell phone use could lead to cancer has continued to grow.  Many scientists have tried to study the prevalence of cancer in cell phone users and the theoretical possibility that cell phones have carcinogenic properties.  A publication in the International Journal of Radiation Biology examined the various studies and retrospective reviews on this topic and came up with the following conclusions:

  1. Theoretically, the radiofrequencies and power used by cell phones and cell phone antennas are not significant enough to cause cancer.
  2. Most epidemiologic studies of cell phone users have not shown a causal relationship between cell phone use and increased incidence of cancer.
  3. The laboratory and animal experiments related to this question are limited and do not show a strong relationship between exposure to cellular phones and cancer.

Most scientists agree that this topic needs to be studied further to make a solid conclusion.  For now, evidence shows that your beloved iPhone, Droid or other device is much more likely to cause you harm because of its ability distract you (leading to a car accident) than by causing cancer.

Terminology: What is Benign, Malignant, Stage, Grade, Differentiation (Carcinoma/Adenocarcinoma/Sarcoma)??

Benign: A tumor that does not have the properties of cancer.  A benign tumor is a growth of tissue that does not grow aggressively, does not invade into adjacent tissue (it can grow and cause pressure on surrounding tissues, but does not actually grow into the tissues themselves) and does not spread to other distant parts of the body.

Malignant: A tumor that this malignant is cancerous by definition.  This tumor has the ability to grow into other surrounding tissues and to metastasize (i.e. spread via the blood or lymph system) to distant parts of the body (e.g. from lung to bone).

Stage: Staging for cancer is a method of categorizing patients into different groups, or stages, based upon characteristics of their tumor in an effort to give the physician a general idea of how “advanced” the cancer is.  Each type of cancer (for example breast, prostate, colon) has different guidelines that categorize this tumor into a particular stage (see the diagram below for an example of colon cancer staging).  Rather than lull you to sleep with the guidelines for staging each type of cancer, we will review the basic principles of the staging.

Stage is typically based on three characteristics of the tumor:

1. Size/extent of the tumor

2. Lymph node involvement (and if so, number of nodes involved)

3. Metastasis, or spread to other parts of the body from where it originated

Cancers are usually staged from I to IV.  In general (although not followed by all types of cancer): Stage I cancer is usually limited to a local area and has not yet infiltrated other immediate structures, the lymph nodes, of distant areas of the body.

  • Stage IV generally means the cancer has metastasized, or spread to a totally different area of the body.
  • Stages II and III occupy the middle ground between the two, and usually include cancers which have infiltrated other neighboring tissues.
  • For more information on the staging guidelines for each type of cancer, go to the American Joint Committee on Cancer’s website, http://www.cancerstaging.org/mission/whatis.html.

Grade and Differentiation: The grade of a tumor can only be determined by a physician specialist, called a pathologist, looking at a small piece of the tumor under a microscope.  To oversimplify the process, the pathologist determines how different the tumor cells are from normal cells (comparing it to the normal cells the cancer mutated from).  We call this degree of mutation the “differentiation” of the tumor.  Pathologists spend a lot time looking at cells under a microscope and are great at recognizing and classifying them.  Cells that look like relatively normal, healthy cells are called “well-differentiated” and cells that look very different from the original tumor are called “poorly-differentiated.”

This naming system sounds a bit counter-intuitive without understanding what the term “differentiation” means.  Normal cells are considered to be highly-differentiated because they have developed unique characteristics that make them different from other cells in the body (for example, a skin cell looks and acts differently than a neuron). Cancer cells, by nature, lose some of these defining characteristics, thus making them less differentiated than normal cells.  When the pathologist looks under the microscope, the level of differentiation of a tumor tells physicians how aggressive the tumor is and how likely it is to grow wildly and spread to other parts of the body.

Tumor types:

Carcinoma: Tumors that arise from epithelial cells.  These include breast, prostate, lung and cancer, among others.

  • Adenocarcinoma: Tumors that arise from gland-forming cells.

Sarcoma: Tumors that arise from connective tissue cells.  Examples include bone, tendon, and cartilage (see the MRI image to the right for an example of a Ewing’s sarcoma which can be seen in the middle of the femur on the left…feel like a radiologist yet?).

Lymphoma and Leukemia: Tumors that arise from hematopoietic cells (a.k.a. the cells of the blood).

Treatment options: Oncology treatment currently consists of a slash (surgery), burn (radiation) and poison (chemotherapy) approach to therapy.

Surgery: In the majority of cases, the goal of surgery is to remove the tumor.  In an ideal situation, the tumor is confined to the tissue from which it arose, making removal of the tumor relatively simple.  Many times, the tumor invades into adjacent structures (other organs, veins, arteries, nerve bundles, etc), and the goal of surgery becomes removing as much of the tumor as possible.  An important concept in surgical oncology is the importance of removing a “margin” around the tumor (i.e. a little extra room around all the sides of the area the surgeon removes)—the larger the margin, the more confident oncologists can be that all of the cancer cells were in fact removed.

Chemotherapy: This term refers to the use of drugs to kill cancer cells.  As the field of cancer research grows, this definition encompasses more classes of drugs.  Historically, the drugs we used to target cancer cells are toxic chemicals that preferentially kill rapidly growing cells more avidly than slow-growing cells.  Notice the use of the word “more avidly”—these drugs unfortunately also kill normal, non-cancerous cells, particularly the ones that divide rapidly.  Interestingly, many of the well-known side effects of chemotherapy, such as vomiting, weight loss and loss of hair are due to this very effect—the cells lining the gastrointestinal tract and the skin cells that cause hair to grow are some of the fastest growing cells in our bodies and are therefore also killed by the toxins of chemotherapy.

Fortunately, the trend in cancer research is toward drugs that are able to specifically target cancer cells by binding to specific receptors that only the cancer cells have.  This not only allows for better killing of the cancer, but also theoretically eliminates many of the horrible side effects associated with conventional chemotherapy.

Radiation Therapy:  This treatment modality also takes advantage of the rapidly-dividing properties of cancer cells. Conventional radiation therapy consists of daily  radiation treatments that occur for weeks at a time (exact length depending upon the type of cancer being treated).  Radiation is delivered by machines that focus beams of photons (i.e. energy particles) toward the part of the body where the cancer is.  Patients do not feel the radiation nor can they see it (sounds kind of like wizardry, right?). The photons cause damage to cancer cells by damaging the DNA of a cell.  Each day, a fraction of the total dose of radiation is delivered to the tumor and often to some of the surrounding tissues.  The cancer cells, due to their broken command center, are unable to repair the damage to their DNA cause by the radiation before the next dose of radiation is given the following day.  Over the course of weeks, this leads to death of the cancer cells and preferential survival of the normal surrounding cells that also received the radiation dose but are able to repair their DNA.

A Cure: Is there hope?

Put simply, yes.  Stay tuned for the next article in our Oncology Series providing information from the cutting edge of cancer research discussing the hope for a cure on the horizon.

Questions? E-mail the Author: erickson@myhousecallmd.com

1. JE Moulder‌, KR Foster, LS Erdreich, and JP McNamee.  “Mobile phones, mobile phone base stations and cancer: a review”.  International Journal of Radiation Biology. 2005, Vol. 81, No. 3, Pages 189-203.


07 2010

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