Dr. Benjamin Jin, a biologist working on immunotherapy for HPV+ cancers, holds test tubes as he works in the lab of Dr. Christian Hinrichs, an investigator at the National Cancer Institute at the National Institutes of Health (NIH) in Bethesda, Maryland, February 7, 2018.
Experimental trials are ongoing at the National Institutes of Health Clinical Center, a US government-funded research hospital where doctors are trying to partially replace patients' immune systems with T-cells that would specifically attack cancers caused by the human papillomavirus (HPV), a common sexually transmitted infection. A person's T-cells will naturally try to kill off any invader, including cancer, but usually fall short because tumors can mutate, hide, or simply overpower the immune system.
Immunotherapies that have seen widespread success, such as chimeric antigen receptor (CAR-T) cell therapies, mainly target blood cancers like lymphoma, myeloma and leukemia, which have a tumor antigen -- like a flag or a signal -- on the surface of the cells so it is easy for immune cells to find and target the harmful cells. But many common cancers lack this clear, surface signal. Hinrichs' approach focuses on HPV tumors because they contain viral antigens that the immune system can easily recognize.
 / AFP PHOTO / SAUL LOEB        (Photo credit should read SAUL LOEB/AFP/Getty Images)
SAUL LOEB/AFP/AFP/Getty Images
Dr. Benjamin Jin, a biologist working on immunotherapy for HPV+ cancers, holds test tubes as he works in the lab of Dr. Christian Hinrichs, an investigator at the National Cancer Institute at the National Institutes of Health (NIH) in Bethesda, Maryland, February 7, 2018. Experimental trials are ongoing at the National Institutes of Health Clinical Center, a US government-funded research hospital where doctors are trying to partially replace patients' immune systems with T-cells that would specifically attack cancers caused by the human papillomavirus (HPV), a common sexually transmitted infection. A person's T-cells will naturally try to kill off any invader, including cancer, but usually fall short because tumors can mutate, hide, or simply overpower the immune system. Immunotherapies that have seen widespread success, such as chimeric antigen receptor (CAR-T) cell therapies, mainly target blood cancers like lymphoma, myeloma and leukemia, which have a tumor antigen -- like a flag or a signal -- on the surface of the cells so it is easy for immune cells to find and target the harmful cells. But many common cancers lack this clear, surface signal. Hinrichs' approach focuses on HPV tumors because they contain viral antigens that the immune system can easily recognize. / AFP PHOTO / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)
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Actress Marcia Cross has been public about her anal cancer diagnosis for more than a year. Now she says doctors suspect her cancer came from the same type of human papillomavirus, or HPV, that’s behind her husband’s throat cancer.

Cross, who completed radiation and chemotherapy and is in remission, wants to raise awareness and end shame surrounding anal cancer – which has been on the rise over the past several decades, according to the National Cancer Institute.

“I know that there are people who are ashamed,” Cross, 57, said on “CBS This Morning.”

“You have cancer. Should you then also feel like ashamed like you did something bad because it took up residence in your anus?”

A broader look at HPV and cancer shows that, while anal cancer is uncommon, Cross’ case is in some ways typical.

HPV is behind the majority of cases

HPV is linked to 91% of anal cancers in the United States, according to the US Centers for Disease Control and Prevention. Women are diagnosed with these cancers at a median age of 62. For men, it’s 59.

The most common type of anal cancer, squamous cell carcinoma, originates in the cells lining the anal canal, according to the US National Library of Medicine. Typically, anal cancer spreads slowly and, if caught early, is often curable.

Nationally, there are more than 6,500 new HPV-associated anal cancer diagnoses each year – including about 4,300 in women and 2,200 in men, according to one agency estimate based on data from 2011 to 2015. That comes out to roughly a couple of cases for every 100,000 people.

About the virus

There are 150 types of HPV, but most are rare and only 14 are considered high-risk for cancer.

“Most people – about nine in 10 – will get an HPV infection at some point in their lives,” the CDC says. It’s the most common sexually transmitted infection in the country, can be spread even when someone has no symptoms, and may result in symptoms years after being exposed to the virus.

HPV infections mostly go away on their own, but some remain and can cause cervix, vagina and vulva cancer in women; penile cancer in men; and genital warts, anal cancer and head and neck cancers in both sexes. HPV-associated cancers are more likely to occur in the throat and cervix than the anus.

Other risk factors for anal cancer include HIV, smoking, and any medications or conditions that might weaken the immune system.

The most likely type of HPV implicated in anal cancer is HPV 16, which is covered by current vaccination.

Current CDC recommendations call for HPV vaccination for boys and girls to begin between the ages of 11 and 12, though the regimen can occur as early as age 9.

When it comes to screening, the jury’s out

While the HPV vaccine and routine screening have made cervical cancer “one of the most preventable cancers,” as the CDC says, the jury’s still out on who should be screened for anal cancer, when and how.

Anal cancers are sometimes found through rectal exams – part of a routine pelvic exam by a gynecologist, in Cross’ case. These cancers may cause symptoms like pain or bleeding, but they often don’t in earlier stages.

“I was so not thinking anything was wrong because I didn’t have any symptoms, and she gave me an exam and came around and said, ‘Well, I just want you to know, whatever it is, it’s curable,’ ” Cross said. “It was like ‘What? What are you talking about?’ “

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The American Cancer Society says that certain groups at higher risk – like recipients of an organ transplant and men who have sex with men – might benefit from a screening measure like the “anal pap,” which looks for precancerous cellular changes when the anus is swabbed. But there’s no widely accepted recommendation.

Treatment options include radiation, chemotherapy and surgery – though the outcome may depend on a number of factors including how large the cancer has become, where it might have spread and what other health issues a patient has.

When compared to people who don’t have cancer, people diagnosed with anal cancer are about 67% as likely to live at least five years beyond their diagnosis. But that ranges from 30% for those with distant metastases to 82% for those with only localized cancer, according to the American Cancer Society.

CNN’s Lisa Respers France and Sandee LaMotte contributed to this report.