What is cancer?
Cancer is a disease caused by cells in the body that grow and multiply out of control. These cells replace normal cells in the tissue or blood. Often, they grow to form a lump or tumor. Tumors may be benign (not cancer) or malignant (cancer).
The type of cancer is named for the organ where the tumor cells first begin to grow. For example, cancer that begins in the lung is called lung cancer. As the tumor gets larger, it can grow into nearby tissues and organs. This may prevent the tissue or organ from working properly.
Cancer cells can also break away from the tumor and spread to other parts of the body. This process is called metastasis. 
Are all cancers the same?
No two cancers are exactly the same, even when they are cancers of the same organ. The differences have to do with what is called the “biology” of the disease. While there are general ways in which cancers are similar, it means that each cancer has its own characteristics that make each person react differently to the cancer and its treatment.
The tendency of cancer cells to grow, divide into more cancer cells, and spread to other parts of the body varies among cancers. These differences in growth and spread of a cancer have a lot to do with how each one is treated. 
Cancers that grow slowly and do not spread easily often can be treated by simply removing the tumor. Other cancers that tend to grow rapidly and spread easily may need treatment of the original tumor and of the whole body. These treatments could include surgery, radiation therapy and chemotherapy.
What do the names of cancers mean?
Cancers are named in several different ways. This can be confusing. Most cancers are named for the organ where the cancer started
• Breast cancer starts in the cells of the breast. Lung cancer starts in the cells of the lung.

• Cancers may also be named for the type of cell that is cancerous in the organ.

• There are breast cells that produce milk in the lobules. If these lobule cells become cancerous, the cancer is called lobular cancer of the breast.

• When a cancer spreads from where it started to another part of the body, it keeps the same cancer name.  When breast cancer spreads to the bone, it is still called breast cancer that has metastasized to the bone.

• Cancers also may have names that do not have anything to do with where the disease started. Sometimes cancers are named for the physician who first described it.

• Hodgkin’s disease is named for the doctor who described the disease

• Other cancers are named for the type of cell the cancer cells resemble.

• An example of this is synovial cell sarcoma, which does not start in the tissue called synovium, but the cells look like synovial cells.
What causes cancer?
Scientists now know that cancer begins in our DNA. A cell can begin to grow out of control and become cancerous growing into a tumor when there is a change in the cell’s genes and its DNA. 
DNA, deoxyribonucleic acid, is the chemical in a gene that carries instructions telling cells what to do.  The instructions in a gene’s DNA are in a complex code. The code can differ in its order or sequence. How the code is sequenced determines the set of instructions given to the cell. 
Other parts of your DNA act to switch genes on or off. This is important because, even though all of your cells carry the same genes, individual cells in different parts of the body will use some genes but not others depending on their job. For example a liver cell has a different job in the body than a lung cell.
The change or mistake within the DNA’s instructions is called a mutation. A mutation can also occur if a mistake is made as the gene’s DNA copies itself when a cell divides. These changes or mutations may lead to the cell growing out of control, causing damage to surrounding tissues.
It generally takes the buildup of several different mutations to result in cancer. These mutations may occur at random or they may be caused by environmental factors such as ultraviolet radiation from the sun, exposure to viruses or from lifestyle choices, such as smoking. 

Most gene mutations are acquired throughout life.
What is a gene?
A gene contains the body's hereditary (passed on from parent to child) information. Its purpose is to give instructions, or a recipe, to a cell to make vital protein molecules. Proteins control how tissues and organs are structured, work and are regulated.
Genes are found on long strands made up of deoxyribonucleic acid (DNA). DNA is formed by a sequence of four chemical bases lined up in a row and linked together like a twisted ladder. The sequence, or order, of these bases determines the information available for building and maintaining the body. (This is similar to letters of the alphabet appearing in a certain order to form words and sentences.)
Any change in the order of chemical bases has an impact on the proteins made. This, in turn, affects the body and how it functions.
What is a gene mutation?
A gene mutation is a permanent change in the sequence of chemical bases in a cell's DNA. Any change in the gene causes one or more of the proteins it directs to function incorrectly or not at all. This, in turn, prevents the cell from working properly and can cause diseases such as cancer. Gene mutations can be inherited from a parent or acquired during a person's lifetime.
How are genes related to cancer?
Genes instruct the cells of the body to make proteins that are vital to its normal functioning. Each cell depends on thousands of proteins to do their jobs in the right place at the right time.
A change in a gene (mutation) that alters a protein can cause the protein to malfunction or be missed entirely. If the protein plays a critical role, this will prevent the cell or organ from developing or functioning properly. It may also cause diseases such as cancer.
What is the difference between oncogenes and tumor suppressor genes?
Genes have two major roles in cancer. Some genes, called oncogenes, can cause cancer. These are normal genes that have mutated and now cause cells to grow out of control.
Other genes, known as tumor suppressor genes, typically help stop cancer from developing or growing. These are normal genes that slow down cell division, like the brake pedal in a car. When tumor suppressor genes don't work properly, cells can grow out of control. That can lead to cancer.
Does each gene mutation cause a certain type of cancer?
No. Scientists have learned that different tumor types may share the same gene mutation that causes the different tumors to develop and grow. For example, some lymphoma and lung cancers share changes in a gene called ALK. Some breast and gastrointestinal cancers share changes in a gene called HER2.
What is genotyping?
Genotyping is a test done to find changes in a person's genes (mutations) that can cause cancer cells to develop and grow. It is done on a small piece of the tumor in the laboratory.
Knowing the unique genetic makeup of a tumor can help your doctor prescribe the best medicine and in the right dose. This will boost the effectiveness of the treatment and minimize possible side effects.
What is the difference between genotyping and genetic testing?
Genotyping is a test done to find changes in a person's genes (mutations) that can cause cancer cells to develop and grow. It is done on a small piece of the tumor in the laboratory and helps your doctor determine the best treatment.
Genetic testing combines a) a study of a person's medical and family history with b) a blood test done on normal cells that identifies changes in chromosomes (part of a cell that contains genetic information), genes or certain proteins of interest.
Genetic testing is used to find changes that are known to go along with inherited medical conditions. The results can confirm or eliminate a suspected genetic condition. These tests can also help determine your future chance of developing a condition or passing it on to your children. An accurate genetic test can tell if a mutation is present, but that finding does not guarantee that disease will develop.
Does genotyping affect the cancer treatment I receive?
It may affect your treatment. Suppose genotyping identifies gene mutations on a tumor. In some cases, certain drug therapies can be used to target that tumor and stop its growth. The targeted therapies are chosen because they are known to be effective for that type of gene mutation in that tumor. Targeting the tumor causes minimal damage to healthy cells.
What is targeted therapy?
Scientists are now able to discover molecular targets within cancer cells. This information allows them to design drug treatments that disrupt the activity of these targets without interfering with normal cells. Targeted therapy, then, uses drugs or other substances to identify and attack specific cancer cells.
What is personalized cancer care?
Personalized cancer care is looking at each individual’s cancer and finding what molecular change has occurred in the cell to cause cancer. By comparing an individual’s normal cell with one of their cancer cells, the specific change that makes the cancer cell different from a normal cell can be identified.

A targeted therapy can be designed to interfere with a specific gene, pathway or process in a tumor. In this way, they hurt the tumor's ability to grow, divide and spread. 
How are targeted therapies different from traditional chemotherapy?
With traditional chemotherapy, the drugs work by killing all rapidly growing and dividing cells. That often leads to unwanted side effects, such as hair loss or low blood cell counts.
In contrast, targeted therapies are designed to target and interfere with a specific gene, pathway or process in a tumor. In this way, they hurt the tumor's ability to grow, divide and spread.
Treatment with targeted therapies is more precisely aimed at the tumor than with traditional chemotherapy. Because normal cells are not affected, targeted therapies usually have fewer and less harmful side effects. 
Can every cancer patient benefit from genotyping and targeted therapies?
Since various forms of cancer have been found to share common tumor mutations, cancer researchers are learning to use targeted drugs across multiple tumor types. Not all genes, mutations or abnormal cell processes in cancers have been identified.
However, research is continuing at a fast pace. In the future, it is expected that genotyping and targeted therapy will be used to help even more cancer patients with other tumor types.
The Massachusetts General Hospital’s Translational Research Laboratory is currently able to screen for more than 130 gene mutations commonly found in patients’ tumors. The Massachusetts General Hospital was the first institution to provide this level of tumor genotyping in a clinical setting.  
Why do some individuals respond to a targeted therapy and others do not?
Scientists are learning how differences in a person's genes affect the body's response to drugs. This information is used in targeted cancer therapy to decide on the best drug program for a person's tumor. Studying the specific genes in a person's tumor helps doctors identify the drug combination to which the tumor will most likely respond.
Can my tumor develop resistance to targeted therapies?

Yes. In some cases, the drugs work well at first and then appear to stop working. Possible reasons for this include:

There is more than one pathway to activate (turn on) the tumor gene.

The cancer cells can "outsmart" the targeted therapy by making changes in their DNA. Then some of the cancer cells survive and continue to grow even though you received treatment.

Other pathways develop that "rescue" the tumor from the targeted therapy’s ability to kill the cancer cells.

These are reasons why combination therapy (combining two or more methods of treatment) and repeat biopsy (removal of cells or tissue for examination) for genotyping are often important.

Why is combination therapy important?
Combination therapy with targeted drugs has been shown to prevent or delay drug resistance in at least two clinical trials. Mass General is now studying more than a half dozen drug combinations to address the problem of drug resistance.

How can we help?

Contact the Cancer Center to learn more about the testing and treatment options at Mass General.
  • Call 617-726-0808

How do I get tested?

Getting tested in one of the first steps in learning what targeted therapy may work for you. 

Learn more about how to get tested.

NCI Dictionary

If you are uncertain about a term used on this website, the glossary of the National Cancer Institute is an excellent resource.