Introduction

Improving cancer care and prevention are high priorities for the American Society of Clinical Oncology (ASCO), the leading society of medical professionals who treat people with cancer. For that reason, ASCO has developed patient resources, such as the Cancer Advances series, to help consumers become better educated about various aspects of cancer, including its prevention, screening, diagnosis, treatment, and care.

This issue of Cancer Advances focuses specifically on the relationship between viruses and cancers. More than a dozen viruses have been associated with specific types of cancer. Researchers are still learning how a cell that is infected with a virus becomes a cancer cell and continue to make discoveries that lead to better methods to prevent, diagnose, and treat viral cancers.

According to Bruce E. Johnson, MD, Director of the Lowe Center for Thoracic Oncology at Dana-Farber Cancer Institute in Boston, Mass, and Chair of ASCO's Cancer Communications Committee, this topic is becoming more important as an increasing number of viruses and infectious agents that have a direct link to cancer are being identified.

The information contained in this publication was presented at an ASCO Meet the Experts session held in New York City in December 2003. This event covered information about the incidence, risk, infection process, prevention, screening, and treatment of the following cancers that are linked to viruses or bacteria.

• Hepatitis B and C and liver cancer
  
  
• Cancers associated with the human papilloma virus
  
  
• Helicobacter pylori and stomach cancer
  
  
• Viruses associated with leukemia and lymphoma
  
  
• Viruses associated with Kaposi's sarcoma

The information contained in this publication is not intended as medical advice or as a substitute for a doctor's opinion. ASCO does not endorse any products or companies mentioned in this publication.

About Viruses

Viruses cause infections that can lead to disease. A virus is a set of genes surrounded by a coat or shell of protein. Viruses are tiny; they can only be seen through powerful, specialized microscopes. "Viruses can contain different amounts of genetic information, anywhere from five genes in a very, very small virus or up to 100 genes in a large herpesvirus. As a reference, humans have probably 35,000 or more genes," explained James J. Goedert, MD, Chief of the Viral Epidemiology Branch and Senior Investigator at the National Cancer Institute in Bethesda, Md.

Viruses cannot make more viruses (replicate) by themselves. They need to first get inside (infect) a living cell, such as those in animals, humans, or bacteria (a host). During replication, the virus creates copies of itself called virions. The infectious virions are released from the cell, typically killing the host cell in a process called lysis. The virions can now infect nearby cells and spread to other people.

Viruses can also be inactive (latent) for many years, meaning they do not cause any symptoms right away. Sometimes these viruses are multiplying, but remain hidden from the body's immune system. Often, latent viruses require additional factors to become "reactivated" and cause infection.

Scientists classify viruses as DNA (deoxyribonucleic acid) viruses or RNA (ribonucleic acid) viruses. DNA and RNA are similar chemicals that store genetic material.

Viruses and Cancer

Viruses were first recognized as disease-causing agents at the close of the nineteenth century. Additional discoveries in the twentieth century showed that viruses could lead to a number of cancers in animals and humans.

"There are several known human cancer-associated viruses," said Dr. Goedert. "The first viruses associated with cancer were discovered in 1964—Epstein-Barr virus (EBV) was one, and the hepatitis B virus (HBV) was then found in 1970."

Established Viral Causes of Cancer:

• HBV and hepatitis C virus (HCV) and liver cancer
  
  
• Human papillomavirus (HPV) and anal, cervical, and head and neck cancers
  
  
• Human T cell leukemia virus type 1 (HTLV-1) and adult T cell leukemia and lymphoma (ATLL)
  
  
• Human herpesvirus-8 (HHV-8) and Kaposi's sarcoma (KS)
  
  
• EBV and Hodgkin lymphoma

Potential Virus-Cancer Links Currently Being Studied:

• HCV and some types of non-Hodgkin lymphoma
  
  
• Polyomaviruses in multiple cancers
  
  
• JC Virus–brain and colon cancers
  
  
• BK Virus–brain cancer
  
  
• SV40 Virus–brain, pituitary, bone, and thyroid cancer, non-Hodgkin lymphoma, and mesothelioma (a form of lung cancer)
  
  
• Breast cancer and a human virus similar to the mouse mammary tumor virus (MMTV)

Identifying, treating, and even possibly preventing cancers caused by viruses is an ongoing challenge because each virus causes cancer through a different process. In addition, some viruses cause cancer indirectly. For example, because HIV reduces the ability of the immune system to protect against illness, people infected with HIV are less able to fight off other infections that lead to cancer.

Prevention, Screening, and Treatment

Viruses that cause cancer are a natural target for prevention and screening efforts, which include the following strategies:

• Stopping the spread of the virus
  
  
• Preventing infection in the first place, such as vaccines for hepatitis B
  
  
• Screening for the virus, which is beginning for HPV and cervical cancer

Doctors also hope that treating a viral infection will also treat the cancer. For example, certain therapies have been proven to reduce the number of Kaposi's sarcoma and non-Hodgkin lymphoma cases among people with acquired immune deficiency syndrome (AIDS).

According to Dr. Goedert, understanding the relationships among viral infection, immunity, and the genetics will help doctors understand more about the viral causes of cancer, and how to develop effective early diagnosis and prevention methods. And, developing other safe and effective therapies that target viruses will help lower the number of cancers that are associated with viruses.

Last Updated: September 27, 2004

| Next >