Breast cancer could be sexually transmitted, says a researcher who has found the same virus that causes cervical cancer in breast cancer tumours from Australian women.

Emeritus Professor James Lawson of the University of New South Wales and colleagues have found the same form of the human papillomavirus (HPV) associated with cervical cancer in almost half the breast tumour samples they tested.

It's the first study of its kind in Australia, although international studies have also found cervical cancer-related HPV in breast cancer cells.

He says while the evidence is far from conclusive, "it's possible and totally worthy of investigation" to suspect that HPV could also cause breast cancer.

Lawson says it's possible that HPV is spread by sexual activity or during showers or baths, when the virus could be transferred from the genital area to the breasts via the nipple ducts.

"We know that the virus explodes out of the cell and is spread by touch, so it's fairly obvious that it could be spread by sexual activity to the breast, you could also argue that it would be spread by washing and bathing," he says.

Lawson says more research is needed to establish whether HPV is actually causing the breast cancer or if women with breast cancer are more prone to infection with the virus.

Younger women

Lawson and colleagues last year published the results of a DNA analysis which found 24 out of 50 breast cancer samples also tested positive for HPV 18, the same form of the virus implicated in cervical cancer.

A subsequent review, published in the journal Future Microbiology in June this year, found various forms of high-risk HPV had been identified in 10 separate breast cancer studies since 1999.

In a letter published online in the British Journal of Cancer last month Lawson reports that a review of the 2005 study found women with HPV positive breast cancers were on average about eight years younger than those whose tumours did not test positive to the virus.

He says this lends weight to the sexual transmission theory, because HPV is more common in younger women who are more likely than older women to have had multiple sexual partners, something he describes as a "post-pill phenomenon."

Lawson says it isn't the first time a virus has been associated with breast cancer.

The mouse mammary tumour virus, which causes breast cancer in mice, has been known about since the 1930s, and in a 2004 study Lawson reported finding a genetically similar version of the virus in Australian women.

Lawson says if it's true that HPV can cause breast cancer as well cervical cancer, the introduction of the cervical cancer vaccine, developed by Australian of the Year Professor Ian Frazer, should also cut rates of breast cancer.

He says he is currently pushing for a study into this.

Doubts raised

But the chief executive officer of Cancer Council Australia, Ian Olver, says while it's possible that a virus could cause breast cancer, the existing studies are small and inconclusive.

"What we've got is small studies that have found an association between HPV and breast cancer … but they haven't shown anything that could say it's causal," he says.

"I think you need much bigger studies and a mechanism by which HPV was implicated in the development."

A recent article published online ahead of appearing in the journal The Breast failed to find evidence of HPV in a study of 81 Swiss women.

"Our analysis could not support a role of HPV in breast carcinoma," the study concludes.