Targeted Cancer Therapies: Questions and Answers

Key Points 

• Targeted cancer therapies use drugs that block the growth and spread of cancer by 

interfering with specific molecules involved in carcinogenesis (the process by 

which normal cells become cancer cells) and tumor growth (see Questions 1, 

2, and 3). 

• Because scientists call these molecules “molecular targets,” therapies that 

interfere with them are sometimes called “molecular-targeted drugs,” 

“molecularly targeted therapies,” or other similar names (see Question 1). 

• The National Cancer Institute’s Molecular Targets Development Program is 

working to identify and evaluate molecular targets (see Question 6). 

1. What are targeted cancer therapies?

Targeted cancer therapies use drugs that block the growth and spread of cancer. They 

interfere with specific molecules involved in carcinogenesis (the process by which 

normal cells become cancer cells) and tumor growth. Because scientists call these 

molecules “molecular targets,” these therapies are sometimes called 

“molecular-targeted drugs,” “molecularly targeted therapies,” or other similar names. By 

focusing on molecular and cellular changes that are specific to cancer, targeted cancer 

therapies may be more effective than current treatments and less harmful to normal cells. 

Most targeted cancer therapies are in preclinical testing (research with animals), but some 

are in clinical trials (research studies) or have been approved by the 

U.S. Food and Drug Administration (FDA). Targeted cancer therapies are being studied 

for use alone, in combination with each other, and in combination with other cancer 

treatments, such as chemotherapy. 

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2. What are some of the cellular changes that lead to cancer?

Normally, cells grow and divide to form new cells as the body needs them. When cells 

grow old, they die, and new cells take their place. Sometimes this orderly process goes 

wrong. New cells form when the body does not need them, and old cells do not die when 

they should. These extra cells can form a mass of tissue called a growth or tumor. The 

cells in malignant (cancerous) tumors are abnormal and divide without control or order. 

They can invade and damage nearby tissues and organs. Also, cancer cells can break 

away from a malignant tumor and spread to other parts of the body. 

Normal cell growth and division are largely under the control of a network of chemical 

and molecular signals that give instructions to cells. Genetic alterations (changes) can 

disrupt the signaling process so that cells no longer grow and divide normally, or no 

longer die when they should. Alterations in two types of genes can contribute to the 

cancer process. Proto-oncogenes are normal genes that are involved in cell growth and 

division. Changes in these genes lead to the development of oncogenes, which can 

promote or allow excessive and continuous cell growth and division. Tumor suppressor 

genes are normal genes that slow down cell growth and division. When a tumor 

suppressor gene does not work properly, cells may be unable to stop growing and 

dividing, which leads to tumor growth. 

To use the metaphor of a car, the presence of an oncogene is like having a gas pedal that 

is stuck to the floorboard, causing cells to continually grow and divide. Tumor 

suppressor genes act like a brake pedal. The loss of a functioning tumor suppressor gene 

is like having a brake pedal that does not work properly, allowing cells to continually 

grow and divide. 

Genetic changes that are not corrected by the cell can lead to the production of abnormal 

proteins. Normally, proteins interact with each other as a kind of relay team to carry out 

the work of the cell. For example, when molecules called growth factors (GFs) attach to 

their corresponding growth factor receptors (GFRs) on the surface of the cell, a process 

carried out by proteins signals the cell to divide. Damaged proteins may not respond to 

normal signals, may over-respond to normal signals, or otherwise fail to carry out their 

normal functions. Cancer develops when abnormal proteins inside a cell cause it to 

reproduce excessively and allow that cell to live longer than normal cells. 

3. How do targeted cancer therapies work?

Targeted cancer therapies interfere with cancer cell growth and division in different ways 

and at various points during the development, growth, and spread of cancer. Many of 

these therapies focus on proteins that are involved in the signaling process. By blocking 

the signals that tell cancer cells to grow and divide uncontrollably, targeted cancer 

therapies can help to stop the growth and division of cancer cells. 

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4. What are some types of targeted cancer therapies?

Targeted cancer therapies include several types of drugs. Some examples are listed 

below: 

• “Small-molecule” drugs block specific enzymes and GFRs involved in cancer cell 

growth. These drugs are also called signal-transduction inhibitors. Gleevec® 

(STI–571 or imatinib mesylate) is a small-molecule drug approved by the FDA to 

treat gastrointestinal stromal tumor (a rare cancer of the gastrointestinal tract) and 

certain kinds of chronic myeloid leukemia (1, 2). Gleevec targets abnormal 

proteins, or enzymes, that form inside cancer cells and stimulate uncontrolled 

growth. Iressa® (ZD1839 or gefitinib) is approved by the FDA to treat advanced 

non-small cell lung cancer. This drug targets the epidermal growth factor 

receptor (EGFR), which is overproduced by many types of cancer cells. Other 

small-molecule drugs are being studied in clinical trials in the United States. 

• “Apoptosis-inducing” drugs cause cancer cells to undergo apoptosis (cell death) 

by interfering with proteins involved in the process. Velcade® (bortezomib) is 

approved by the FDA to treat multiple myeloma that has not responded to other 

treatments (3). Velcade causes cancer cells to die by blocking enzymes called 

proteasomes, which help to regulate cell function and growth. Another 

apoptosis-inducing drug called GenasenseTM (oblimersen), which is only available 

in clinical trials, is being studied to treat leukemia, non-Hodgkin lymphoma, and 

solid tumors. Genasense blocks the production of a protein known as BCL–2, 

which promotes the survival of tumor cells. By blocking BCL–2, Genasense 

leaves the cancer cells more vulnerable to anticancer drugs. 

• Monoclonal antibodies, cancer vaccines, angiogenesis inhibitors, and gene 

therapy are considered by some to be targeted therapies because they interfere 

with the growth of cancer cells. Information about these treatments can be found 

in the following National Cancer Institute (NCI) fact sheets, which are available 

on the Internet or by calling the Cancer Information Service (CIS) (see below): 

—Biological Therapies for Cancer: Questions and Answers includes information 

about monoclonal antibodies and cancer vaccines. This fact sheet is available at 

http://www.cancer.gov/cancertopics/factsheet/Therapy/biological on the Internet. 

—Herceptin® (Trastuzumab): Questions and Answers contains information 

about Herceptin, which is a monoclonal antibody. This fact sheet can be found at 

http://www.cancer.gov/cancertopics/factsheet/Therapy/herceptin on the Internet. 

—Angiogenesis Inhibitors Therapy: Questions and Answers is available at 

http://www.cancer.gov/cancertopics/factsheet/Therapy/angiogenesis-inhibitors on 

the Internet. 

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—Gene Therapy for Cancer: Questions and Answers can be found at 

http://www.cancer.gov/cancertopics/factsheet/Therapy/gene on the Internet. 

5. What impact will targeted therapies have on cancer treatment?

Targeted cancer therapies will give doctors a better way to tailor cancer treatment. 

Eventually, treatments may be individualized based on the unique set of molecular targets 

produced by the patient’s tumor. Targeted cancer therapies also hold the promise of 

being more selective, thus harming fewer normal cells, reducing side effects, and 

improving the quality of life. 

6. What are some resources for more information?

The NCI’s Molecular Targets Development Program (MTDP) is working to identify and 

evaluate molecular targets that may be candidates for drug development. As part of the 

NCI’s Center for Cancer Research, the MTDP provides research support for 

NCI-designated, high-priority drug discovery, development, and research focused on 

specific molecular targets, pathways, or processes. The MTDP’s Web site is 

http://home.ncifcrf.gov/mtdp/ on the Internet. 

Information about clinical trials is available from the CIS (see below). Information 

specialists at the CIS use PDQ®, the NCI’s cancer information database, to identify and 

provide detailed information about specific ongoing clinical trials. PDQ includes all 

NCI-funded clinical trials and some studies conducted by independent investigators at 

hospitals and medical centers in the United States and other countries around the world. 

People also have the option of searching for clinical trials on their own. The clinical 

trials page of the NCI’s Web site, located at http://www.cancer.gov/clinicaltrials/ on the 

Internet, provides information about clinical trials and links to PDQ. 

Selected References 

1. Demetri GD, von Mehren M, Blanke CD, et al. Efficacy and safety of imatinib mesylate 

in advanced gastrointestinal stromal tumors. New England Journal of Medicine 2002; 

347(7):472–480. 

2. Kantarjian H, Sawyers C, Hochhaus A, et al. Hematologic and cytogenetic responses to 

imatinib mesylate in chronic myelogenous leukemia. New England Journal of Medicine

2002; 346(9):645–652. 

3. Richardson PG, Barlogie B, Berenson J, et al. A phase 2 study of bortezomib in relapsed, 

refractory myeloma. New England Journal of Medicine 2003; 348(26):2609–2617. 

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# # # 

Related NCI materials and Web pages: 

• National Cancer Institute Fact Sheet 2.11, Clinical Trials: Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/Information/clinical-trials) 

• National Cancer Institute Fact Sheet 7.2, Biological Therapies for Cancer: Questions 

and Answers (http://www.cancer.gov/cancertopics/factsheet/Therapy/biological) 

• National Cancer Institute Fact Sheet 7.18, Gene Therapy for Cancer: Questions and 

Answers (http://www.cancer.gov/cancertopics/factsheet/Therapy/gene) 

• National Cancer Institute Fact Sheet 7.42, Angiogenesis Inhibitors Therapy: 

Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/Therapy/angiogenesis-inhibitors) 

• National Cancer Institute Fact Sheet 7.45, Herceptin® (Trastuzumab): Questions and 

Answers (http://www.cancer.gov/cancertopics/factsheet/therapy/herceptin) 

• What You Need To Know AboutTM Cancer—An Overview

(http://www.cancer.gov/cancertopics/wyntk/overview)

For more help, contact: 

NCI’s Cancer Information Service 

Telephone (toll-free): 1–800–4–CANCER (1–800–422–6237) 

TTY (toll-free): 1–800–332–8615

LiveHelp® online chat: https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 6/13/06 

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