What to Know About HPV, the Sexually Transmitted Disease that Led to Marcia Cross’ Anal Cancer

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Marcia Cross first shared that she had anal cancer in the hopes of ending the stigma against the disease. But in a new interview, she also urged people to get protected against HPV, or human papillomavirus, the infection that led to her cancer.

HPV is the most common sexually transmitted disease, with 3 million new cases in the U.S. each year. Many people will live their lives without ever knowing that they have HPV, but for some, it can develop into cancer.

For Cross, HPV was how she developed anal cancer, and speaking to CBS This Morning on Wednesday, she revealed that her doctors said her cancer likely came from the same HPV strain that caused her husband Tom Mahoney’s throat cancer nearly a decade earlier.

Dr. Mary Jane Minkin, a board-certified OB/GYN at Yale University School of Medicine and member of PEOPLE’s Health Squad who did not treat Cross or her husband, said that they “would have passed the HPV by sexual contact,” of any kind.

“She may have been carrying it for years,” Minkin says. “You can go your whole life and not know that you have it.”

RELATED: Marcia Cross Learned Her Anal Cancer Likely Caused by Same HPV Strain as Husband’s Throat Cancer

And for many people, they can go their whole life with HPV and not develop cancer.

“HPV does not mean cancer,” Minkin says. “There are about 100 strains of HPV, but not all of them are cancer causing. Some strains cause genital warts, but those aren’t the ones that cause cervical cancer. You could even be with a partner who has it and not get it. And we don’t know why. Some people have this superimmune system and they just fight it off.”

But Minkin says that people should get tested for HPV, and women should get a pap smear every three years.

“If you’re known to be a carrier of high-risk HPV, then you want to get regular pap smears to check for cancer,” she says.

In some cases, though, HPV does turn into cancer. Cervical cancer, which only affects women, is the most common type from HPV, along with throat, anal, vulvar, penile and vaginal cancer.

Cross, who is in remission, said that she’s now urging everyone to get the HPV vaccine, and will start her 12-year-old daughters on the series of three shots in a few weeks. Minkin does the same with her patients – both men and women – ever since the vaccine was introduced about 13 years ago.

“The first shots were good against about 70 percent of strains causing cervical cancer, but the newer vaccines are effective against nine strains of the virus and about 90 percent effective,” she says. “HPV is the most common STD, and we are seeing reductions with the vaccine becoming more readily taken up.”

Minkin says that when the vaccine first came out, there was concern among parents that girls who get it will then become sexually active – “but we certainly have not seen this,” she says. “It has nothing to do with the shot.”

The goal, she says, is to “give the shot fairly early in young girls’ lives to get it to them before they become sexually active.” But also, Minkin says that parents should recognize that they can’t stop their kids from having sex.

“This is a virus that is just out there. When people say to me, oh my daughter’s not having sex, she doesn’t need the shot – trust me, she’s having sex,” she says. “We encourage our patients to get this shot.”

People can also get the shot at just about any age, an update in the last year, though Minkin says it isn’t as necessary in middle age and beyond.

“When the vaccine first came out, the recommendation was to give it to women age 11 to 26, but that was just who the tests had been on in clinical trials, so the insurance companies said that’s what they would cover. But in the last year, that number has been taken away and the top age has been lifted,” she says.

“If you’re unsure if you need the vaccine, talk to your health care provider,” Minkin says.

Minkin also emphasizes that it’s more than one shot – the HPV vaccine requires a series of three shots.

“In the U.S., we have problems with finishing the series and getting all three shots, though there is data that shows that just one or two protects you pretty well,” she says. “You’re not getting the full protection of all three shots though, so I still encourage my patients to get all three. But one or two is better than nothing.”