Genital wart and cervical cancer

Two new scientific studies add to the evidence implicating a sexually transmitted "bug" in the development of penile cancer, a malignancy rare in the United States but more common in Brazil and other Latin American countries.

The organism in question is the human papillomavirus (HPV). Virologists have identified more than 60 different types of HPV, including some that cause harmless warts on the hands and feet. Other types, such as HPV-16 and HPV-18, cause nearly invisible "flat warts" of the genitals. These strains are associated with cervical cancer in women (SN: 6/8/91, p.362) but had not been clearly linked previously to penile cancer.

A study presented last week at the annual meeting of the American Urological Association, held in Washington, D.C., suggests that HPV-16 and HPV-18 may cause up to one-third of all U.S. penile cancers. The new study is the largest to look at HPV and cancer of the penis in the United States.

"HPV is associated with penile cancer," says lead investigator John S. Wiener of Duke University Medical Center in Durham, N.C. "It is the strongest data yet to prove that association," he says.

Wiener and his colleagues began their experiment by obtaining preserved samples of tumors taken from 29 men with cancer of the penis who had been treated at Duke and other medical institutions between 1970 and 1991. Using polymerase chain reaction, a powerful technique that multiplies trace amounts of genetic material, the researchers searched for viral DNA in the tumor specimens.

They discovered DNA characteristic of HPV-16 in eight of the 29 samples, or 28 percent. One man of the 29 had DNA from HPV-18 in his tumor. No sample contained both types of virus, Wiener reported at the meeting.

In six of the 29 cases, the Duke team analyzed tissue taken from the primary tumor as well as from lymph nodes to which the cancer had spread. Three of the six had HPV infection, and each of these three had HPV-16 in both the primary tumor and the cancerous lymph node tissue. That finding hints that the virus plays a role in the genesis of penile cancer and then tags along as bits of the original tumor break off and travel to other parts of the body, Wiener says.

Another research team took a more detailed look at HPV and the spread of penile cancer. Stephen K. Tyring, a virologist at the University of Texas Medical Branch at Galveston, and his colleagues examined tumor tissue taken from one man infected with HPV-16 whose penile cancer had spread to the lymph nodes. Tyring presented his team's data at the urology meeting.

When the Texas team looked at the primary tumor and lymph node tissue, they discovered that the viral DNA had inserted itself into the man's DNA. Furthermore, the viral DNA had been incorporated at exactly the same location in both the primary tumor and the lymph nodes. Those findings suggest the viral DNA probably makes changes in the patient's DNA that may lead to cancer, Tyring says.

Other researchers have made similar observations in studies of cervical cancer; however, this is the first time scientists have demonstrated that DNA from HPV has incorporated itself into a penile cancer patient's DNA.

HPV is not the only factor leading to cancer of the penis, which usually strikes men age 50 and older. The disease is more likely to strike men who become infected with HPV earlier in life. However, many men infected with HPV never get penile cancer, Tyring notes. Researchers know the cancer occurs more frequently in men who are not circumcised and in men who smoke cigarettes. It may be that HPV acts along with some other factor to cause malignant changes in the penis, Tyring speculates.