Published in The Hindu on June 3, 2010
The results of a vaccine trial for preventing breast cancer in mice have raised hopes of finding an effective vaccine for use in humans. Breast cancer is one of the biggest killers in several countries. With nearly 100,000 new cases reported every year in India, it has overtaken cervical cancer as the number one cancer afflicting women. The results published online in the journal Nature Medicine show that none of the genetically breast cancer-prone mice vaccinated with a single dose of alpha-lactalbumin protein developed the cancer while those that received a placebo did. Except for a couple of studies, research has shown the significance of using this protein as a potential antigen for breast cancer. Alpha-lactalbumin is normally not present in non-breast human tissues. Hence to be chosen as a preventive vaccine candidate antigen to prime the immune system, the protein should satisfy certain conditions. It should be expressed by a majority of breast tumours at significant levels that allow its detection. Secondly, its production by normal breast cells should be restricted to certain easily traceable situations. In this case, alpha-lactalbumin, a lactation-dependent milk protein, is expressed only by lactating mothers. Also, there appears to be less likelihood of the prophylactic vaccine causing any harm to vaccinated women because, the authors note, the availability of the protein is “insufficient in normal non-lactating tissue.”
Preventive vaccines against cervical cancer and liver cancers have been approved for use in the United States and in several European countries. But unlike in the case of breast cancer, the approved vaccines are directed against a virus that causes the cancer and not cancer formation itself. Another challenge is that while viruses are easily detected by the immune system, breast cancer cells are normal cells that have turned into rogue cells and hence escape detection and destruction by the immune system. Despite the study showing that the targeted protein lies dormant in the breast tissue in non-lactating mothers and therefore poses less risk of destroying normal cells through vaccination, the need to collect more supporting evidence before undertaking human clinical trials cannot be over-emphasised. However, if proven safe, a preventive breast cancer vaccine can be administrated to those past child-bearing age. This study is significant for another reason: it has successfully demonstrated in animal trials the criteria to be used for choosing the ideal antigen for cancer prevention vaccines.