Medicine: Breast Cancer and Virus

Of all the diseases to which women are susceptible, few are more devastating than breast cancer. This year alone the disease will affect 70,000 American women and kill 30,000. Doctors who have tried for decades to determine the cause now have strong evidence that a principal villain is a virus. Researchers in the U.S. and India have found high concentrations of virus-like particles in the milk of women with family histories of breast cancer. Equally important, according to an article published in the British scientific journal Nature, they have found that these particles are indistinguishable from viruses known to cause cancer in animals.

The findings represent a major medical discovery. They raise the possibility that doctors might one day be able to immunize women against breast cancer. Doctors have known since 1936 that the Bittner virus can cause cancer in laboratory mice; they learned in 1969 that similar particles could also be found in human milk. It was not until early this year that a direct correlation between the virus-like particles and a familial history of human breast cancer was established.

Indian Findings. What provided the clue was a study by Bombay Drs. S.M. Sirsat, J.C. Paymaster and A.B. Vaidya of the Parsis, descendants of the Zoroastrians who fled Persia 1,200 years ago, settled in India and married exclusively within their own sect. Parsi women are three times more likely to develop breast cancers than the rest of the Indian population. Nearly 40% of the Parsi mothers studied showed virus-like particles in their milk.

The prevalence of such particles is hardly unique to the Parsis. In a study undertaken to test the relevance of the Indian team’s findings, Biophysicist Dan Moore and his colleagues at the Institute for Medical Research in Camden, N.J., analyzed milk from 166 American women. Of 156 with no family history of breast cancer, only seven (5%) showed evidence of the particles in their milk. But of ten women whose families had a history of the disease, six (60%) were found to harbor large numbers of the particles. Doctors are still reluctant to state flatly that these particles actually cause breast cancers in humans. They have been unable as yet to identify particles in a human tumor. But Moore has found that serum from humans who have had breast cancer can have a neutralizing effect on the mouse virus when the serum is injected into mice.

Master Molecule. Even more significant evidence of the agent’s potential threat has been provided by Drs. Sol Spiegelman and Jeffrey Schlom of Columbia University. They report in Nature that a “double blind” study,* conducted both in Camden and at Columbia, showed a 100% correlation between particle concentrations and the presence of an enzyme, or chemical catalyst, which is associated with viruses known to cause cancer in animals. The experiment also revealed two startling similarities between the virus-like particles and tumor-causing RNA viruses: both have the same density and both share the ability to reverse the normal order of genetic transmission. Spiegelman’s and Schlom’s conclusion is crucial. Normally, DNA, the double-helix master molecule, produces RNA, which carries genetic information to the cell (TIME, April 19). But tumor viruses can use their own RNA to produce DNA, which may trigger the cancerous growth that is perpetuated in succeeding cell generations as the affected cell replicates and divides.

The researchers believe their findings indict such particles as a cause of breast cancer, though they are unsure how the agent is transmitted. Mice and rats are known to pass mammary cancer to their young through their milk. No such relationship has yet been found between human nursing and breast cancer. Investigation of that possibility continues.

* So called because the identities of both experimental and control groups are kept secret until after all samples have been analyzed and evaluated.