Sexually transmitted virus strongly linked to risk of breast cancer

February 1, 2016 22:44

Women with abnormal cells on their cervix owing to certain types of human papillomavirus infection are at higher risk of developing breast cancer later in life, the findings from a new study suggest.

More than 100 types of human papillomavirus, more commonly known as HPV, have now been identified, about 10 of which are classified are classified as “high-risk” because they lead to the type of abnormal cell changes that can go on to cause genital or cervical cancers.

But it has been suspected HPV may have a role in the development of some breast cancers. Researchers led by the University of New South Wales reviewed about 4,000 pathology reports from women with benign breast biopsies, but who in later years developed breast cancer.

The researchers identified 30 low-risk and 20 high-risk HPV types in 855 of the breast cancer cases. While not conclusive, the finding strongly supports a growing body of evidence linking HPV to a small subset of breast cancers.

HPV is transmitted to women most commonly through sex with a man and is detected through a pap smear, a test used to detect changes to the cervix that may lead to cervical cancer. While the researchers are unsure how HPV is transmitted from the cervix to the breast, they speculate it might be transmitted by white blood cells throughout the body, including to the breast.

The lead author of the study, Prof John Lawson, said the study found HPV type 18 was the most common type identified in breast cancer specimens, followed by HPV 16. The HPV vaccine, known as Gardasil and which is free for 12- to 13-year-old Australian girls and boys, prevents infection from both HPV types 18 and 16, as well as 6 and 11.

“Gardasil is very effective for those types, and while we don’t have enough evidence to say for sure, Gardasil should be effective at preventing breast cancers assocaiated with those types as well as cervical cancers,” Lawson said.

“Ensuring people receive the vaccine is the obvious and wise thing to do, and that applies to young males as well as they’re involved in the sexual transmission of HPV to women.”

According to Cancer Australia, one in 719 men and one in eight women will be diagnosed with breast cancer by their 85th birthday. Aside from high levels of radiation, there is no known cause of breast cancers. But there are risk factors associated with it, such as being a woman, or mutations in BRCA1 or BRCA2 genes –which leave women with a much higher risk of developing the cancer.

“The evidence which is emerging, and with which our group is intimately involved in, is that a handful of viruses probably cause breast cancer,” Lawson said. “HPV is one of them. The challenge remains to fully understand the role HPV plays in causing breast cancer.”

Some things were known about the link between HPV and breast cancers that may help guide future research, he said, such as that there was a higher prevalence of HPV-related breast cancers in younger women (usually in their 50s), most likely due to their higher rate of sexual activity.

The research was funded by the National Breast Cancer Foundation and its acting chief executive, Jackie Coles, said the importance of research into HPV-related breast cancers came down to prevention.

“In particular, the high-risk HPVs that have been identified in breast cancer are the same types as those for which the cervical cancer vaccine is effective.”

An expert in medical genetics with the University of Newcastle, Prof Rodney Scott, said it appeared HPV accounted for a “very small” proportion of women who developed breast cancer at a younger age. “But given the number of women presenting with breast cancer overall, it is important for further studies to be carried out to prove a relationship,” he said.

“The researchers should continue this work, because an important facet to cancer risk and management is identifying women who may possibly develop the disease.”

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