The Basics of Targeted Therapy

You may hear news reports and talk about “targeted therapy” being the future of cancer treatment. But what does “targeted therapy” mean and how could it help you fight cancer?

To understand how targeted therapies work, you have to learn about cells. Cells are found in all living things.  There are many kinds of cells in the human body.  Each cell can:

  • take in nutrients (foods) needed
  • change nutrients into energy
  • do special functions based on what kind of cell they are
  • make more cells as needed to keep the body healthy.

All cells contain DNA (deoxyribonucleic acid). DNA tells all the cells in your body how to act. It stores information about genetics (what is passed to you by your parents). This “genetic” code causes people to have a certain eye color. It also spells out how all cells will act.

When normal cells become old or damaged, they die. The body replaces them with new cells.   Normal cells go through this life cycle in a very controlled way.  They do this with the help of specific “signaling molecules.”  Signaling molecules help cells share information, or signals, with each other.  Some signaling molecules, called growth factors, tell cells to grow.  Other signaling molecules, called growth inhibitors, tell the cell to stop growing. 

Sometimes, there can be a problem with cell signaling process. DNA found in the cell can become damaged or mutated (changed). This affects how normal cells grow and make new cells (reproduce).  When this happens, cells do not die when they should. New cells are made when the body may not need them.  Over time, these extra cells can form a lump or mass called a malignant tumor, or cancer. 

Cancer can be treated in lots of ways. Doctors use surgery, radiation therapy, chemotherapy and more. Targeted therapies most often are part of chemotherapy. Chemotherapy is treatment using drugs to stop cancer cells from growing. These drugs are most often taken “intravenously,”  which is a needle (IV) put directly into a vein. Chemotherapy can work on all fast growing cells, even normal ones. This is why chemotherapy patients often lose their hair or have issues with taste and smell. 

In the past ten years, new therapies have been developed to treat cancer.  These target cancer cells, not just all fast growing cells.  The drugs attach to cancerous cells to stop their growth and development. 

Researchers have learned about the ways cells communicate. These “pathways” can lead to many types of cancer. Researchers have developed drugs that block those pathways.  These drugs are called “targeted agents.”  When a patient is given these targeted agents to treat cancer, it is called targeted therapy.  Targeted therapy slows or stops cancer cell growth by blocking the way cells communicate with other cells.  It does this by blocking the signals that proteins and other molecules send along the signaling pathways.  As mentioned earlier, these signaling pathways tell the cell to perform basic cell functions such as grow, divide, or die.   

The targeted agents that are most often used today are small molecule drugs or monoclonal antibodies.  These agents are created by researchers in a laboratory. They are designed to find and bind to specific substances found on cancer cells.  Small molecule drugs can pass through the outside of the cell (cell membrane) and act on a target found inside the cell.  Many small-molecule drugs are tyrosine kinase inhibitors.  Tyrosine kinase inhibitors act against cell signaling pathways involved in tumor growth.   Monoclonal antibodies cannot pass through the cell membrane like tyrosine kinase inhibitors.  Instead, they are used against targets that are found on the cell surface.    The FDA (Food and Drug Administration) has approved several targeted agents for the treatment of cancer (see tables 1 and 2). 

Table 1:  Small Molecule Inhibitors for Cancer Treatment

 

Drug/Agents

Generic name (trade name)

Cell

Target

FDA approved

for listed cancer

Bortezomib (Velcade)

26S proteasome

Multiple myeloma, mantle cell lymphoma

Dasatinib (Spryvel)

BCR-ABL, SRC family, c-KIT, PDGFR

Chronic myeloid leukemia (CML), acute lymphocytic leukemia (ALL)

Erlotinib (Tarceva)

EGFR

Non-small cell lung cancer (NSCLC), pancreatic cancer

Gefitinib (Iressa)

EGFR

Non-small cell lung cancer

Imatinib (Gleevec)

BCR-ABL, c-KIT, PDGFR

Acute lymphocytic leukemia (ALL), chronic myeloid leukemia (CML), gastrointestinal stromal tumor (GIST)

Lapatinib (Tykerb)

HER2/neu, EGFR

Breast cancer with HER2/neu overexpression

Sorafenib (Nexavar)

BRAF, VEGFR, EGFR, PDGFR

Renal cell cancer, hepatocellular carcinoma

Sunitinib (Sutent)

VEGFR, PDGFR, c-KIT, FLT3

Renal cell cancer, gastrointestinal stromal tumor (GIST)

 
 

Table 2:  Monoclonal Antibodies for Cancer Treatment

 

Drug/Agents

Generic name (trade name)

Cell

Target

FDA approved

for listed cancer

Alemtuzumab (Campath)

CD52

Chronic lymphocytic leukemia (CLL)

Bevacizumab (Avastin)

VEGF

Colorectal cancer, non-small cell lung cancer (NSCLC) of nonsquamous cell type

Cetuximab (Erbitux)

EGFR

Colorectal cancer, head and neck cancers

Gemtuzumab ozogamicin (Mylotarg)

CD33

Acute myeloid leukemia (AML)

Y-Ibritumomab tiuxetan (Zevalin)

CD20

Non-Hodgkin’s lymphoma

Panitumumab (Vectibix)

EGFR

Colorectal cancer

Rituximab (Rituxan)

CD20

Non-Hodgkin’s lymphoma

I-Tositumomab (Bexxar)

CD20

Non-Hodgkin’s lymphoma

Trastuzumab (Herceptin)

HER2/neu

Breast cancer with HER2/neu overexpression

 

Clinical trials are meant to help improve current treatments (standard of care) or obtain information on new treatments for cancer patients.  Clinical trials are currently being done to see if targeted therapies are safe and effective in different tumor types such as breast, lung, colorectal and blood cancers.  It is important to discuss your treatment options with your doctor and together determine if targeted therapy is right for you.  PearlPoint Cancer Support can also help you find a clinical trial near you.