Cancer is a disease that develops when cells in the body grow and multiply in an uncontrolled manner. These aberrant cells replace normal tissue or blood cells, and often grow to form a lump or tumor. Tumors may be benign (not cancer) or malignant (cancer).

While there are general ways in which cancers of the same organ are similar, no two cancers are exactly alike. The differences have to do with the “biology” of the disease. Each individual’s cancer has its own genetic characteristics. Because of these genetic differences each person responds differently to the cancer and treatments he or she undergoes.

Scientists now know that cancer originates from changes, or mutations, in our DNA, the chemical that carries the instructions for cell functioning. These changes in a cell’s DNA can spur it to divide in an uncontrolled fashion, become malignant and form a tumor, and damage surrounding tissues. A change or mistake in the DNA 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. Cancer usually develops after several different mutations have occurred. 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 not present at birth but are acquired throughout life.

A gene is a long strand of DNA that contains the instructions a cell needs to make vital protein molecules. Proteins control how tissues and organs are structured, work, and are regulated. 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—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 cells produce, which, in turn, affects the body and how it functions.

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.

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 its job correctly and at the right time. A gene mutation can cause the cell to produce too little or too much of a protein, or for a protein to malfunction. If the protein plays a critical role, this will prevent the cell or organ from developing or functioning properly, and can lead to the development of diseases such as cancer.

Traditional chemotherapy kills all rapidly growing and dividing cells and these drugs often causes 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 impair the tumor's ability to grow, divide, and spread. Because normal cells are not affected, targeted therapies usually have fewer and less-harmful side effects.

Results are discussed with clinical and computational experts before they are presented to your doctor, who will go over the findings with you.