Our body is made of cells, trillions of them. Each cell is so small that it can only be seen with a microscope. Cells are essentially tiny balls, all stuck together, and together they make up our organs and do all of the little jobs that keep our body working.
Cells have very important jobs within our body, and different cells have different jobs. And
our cells are very carefully programmed, much like a computer. Computer programs and cells both do their jobs by following written instructions. A computer program is written by typing out hundreds or thousands of lines of instructions.
For a cell, those written instructions are contained in the cell’s DNA. ‘DNA’ is the short form for a chemical called deoxyribonucleic acid.
DNA is an enormous list of instructions. And cancer occurs when the DNA starts giving the wrong instructions.
When Cells Become Cancer
In a cancer cell, the DNA has changed – we use the word ‘mutated’ – in a way that gives the cells different instructions. Changing a line of code in a computer program can cause the program to behave differently, and a change in the DNA code can do the same thing for a cell.
In a cancer cell, the mutations tell the cell to start dividing and not to stop. This can cause problems if they start to overrun the organ where the cancer started, such as the lungs or the liver.
Making matters worse, instead of staying in the location where it’s supposed to be, the cell learns to move. The cancer cell can invade the bloodstream or lymphatic system, travel to other parts of the body, and start growing there.
Cancer cells have other tricks that help them to grow and divide, and these are called the Hallmarks of Cancer. We won't go into these here, but if you are interested in reading exactly how a cancer cell is different from a normal cell, go here.
Cancer is Not One Disease
We talk of ‘cancer’ as being a single disease, but it is not. Cancer is actually hundreds of different diseases under one label. There are many, many types of cancers, including lung, breast, prostate, colon, skin, stomach, brain, bone, and many others.
A cancer can arise from almost any cell in the body. Some cancers are common – such as lung, prostate, breast and colon – and some are rare, like cancers of the muscles or nerves.
All of these different types of cancers behave differently, and they respond differently to treatment. A breast cancer has a different set of genetic instructions than a lung cancer or a colon cancer, so it has different patterns of behavior and spread. Even individual breast cancers, in different patients, will often behave differently.
How Do Doctors Know that I have Cancer?
Most of the time, to make a diagnosis of cancer, doctors need to take a sample of the tumor to examine under the microscope. Taking a sample of tumor is called a biopsy.
Depending on where the cancer is located, your doctor will choose an appropriate approach to get a sample. For a skin cancer, a biopsy is usually very easy because the cancer is visible. The doctor can cut off a little piece, or the whole thing, using some special instruments. Other times, a needle is used to get a biopsy. For prostate cancer, needles are placed into the prostate (usually through the rectum) to get a sample. For a colon cancer, a device passed up into the colon can be used to find the tumor and take a sample.
Regardless of the approach, once a sample is obtained, a doctor will look at it under a microscope. This type of doctor is usually called a pathologist. The pathologist writes a pathology report that describes what they see. Since cancer treatment depends on the type of cancer, the pathology report is one of the most important documents in your medical file. It sets the stage for all the treatment recommendations.
A few types of cancer can be diagnosed without a biopsy, but this is uncommon.
Cancer Comes In Stages
The recommended treatment for a patient with cancer is usually based on two major things:
First, the type of cancer. This is what is determined by looking at the biopsy under the microscope, telling us that it’s a lung cancer, or a breast cancer, or some other type of cancer.
Second, whether the cancer has spread anywhere. The extent of spread of a cancer is called a ‘stage’. Treatments depend on stage.
Most cancers are staged on a scale going from 1 to 4. On that scale, stage 1 usually refers to a small tumor that hasn’t invaded very far, grown too big, or travelled anywhere else. Stage 4 usually refers to a cancer that has spread through the bloodstream to other parts of the body, and stage 2 and 3 are in between, where the tumor is larger than in stage 1, or has spread to some lymph nodes but not to other organs. The staging system varies for each type of cancer.
The stage is critical for determining the treatment path. If you've been given the wrong stage, you might be given the wrong treatment.
How Is Cancer Treated?
Doctors have three main weapons against cancer.
The first is surgery, which involves cutting out the tumor, sometimes along with nearby lymph nodes that might be involved with cancer. The second is radiation, an invisible beam that is aimed at the cancer cells. Surgery and radiation therapy are called ‘local therapies’, because they only work in one location. Surgery is only effective in the area where the surgeon is operating. Radiation treatment only works in the area where the radiation beams hit the cancer cells. (Rarely, radiation can lead to anti-cancer effects elsewhere in the body by activating the immune system, but we won't go into it here)
The third weapon we have is drugs. These drugs are usually given into a vein (intravenously) but are sometimes taken as pills by mouth. Drugs are different than local therapies, because they travel through the bloodstream and circulate throughout the body. Because they travel throughout your whole system, they are called ‘systemic therapy’.
Systemic therapy includes drugs that we call chemotherapy, which tend to also affect some normal cells, newer tailored drugs that are called ‘targeted agents’ that are more specific to targeting the cancer, and a new class of drugs called 'immunotherapy', which try to get the immune system to attack the cancer..
In most cases, systemic therapies by themselves cannot cure a cancer. There are a few exceptions to this rule, like cancers of the immune system (lymphomas and leukemias), and some other tumors that are very sensitive to drugs. For the most part, however, some type of local treatment is usually necessary for a chance of cure.
Want to learn more about the basics? Visit the US National Cancer Institute's "What is Cancer" Website.