A new study has reported that measles virus antigens may be present in a relatively large proportion of breast cancer patients and might contribute to its development. The study was designed to explore the presence and significance of measles virus in breast cancer patients. The authors previously described the presence of the measles virus in biopsies of patients with Hodgkin's lymphoma. Breast cancer is the most common cancer among women in Western countries, having an age distribution with two peaks, at 50 and at 70 years. The causes of breast cancer are varied, including hereditary and hormonal factors. A few viruses have also been reported to be associated with breast cancer, including mammary tumor virus, Epstein-Barr virus and human papilloma virus (HPV).

The study included 131 patients with invasive breast cancer diagnosed between 1998 and 2005. Data was collected concerning age, breast cancer stage, histological grade and the expression of estrogen receptors (ER), progesterone receptors (PR), HER2/neu, p53, and Ki-67. Overexpression of the p53 protein may be involved in cancer development and Ki-67 is a measure of proliferation. The women's tumors were examined for measles virus, based on the presence of measles virus antigens (which typically stimulate an immune response), hemagglutinin (found on the surface of the virus, it binds the virus to the cell that is being infected) and nucleoprotein (protein linked to a nucleic acid, either DNA or RNA).

Hormone receptors were positive (ER+/PR+) in 54% of the tumors and HER2/neu was overexpressed in 18%. Measles virus antigens were detected in 64% of the tumors overall. All biopsies that contained ductal carcinoma in situ (DCIS) had measles virus in the DCIS component as well as in the invasive component. Examining variables one by one, it was found that measles virus correlated with ER+, PR+, low proliferation (Ki-67 index < 40%), low or intermediate tumor grade, age under 50 years, and overexpression of p53. However, when examined together in multivariate analysis, only tumor grade, p53 and age remained associated with the presence of measles virus. The authors conclude that measles virus antigens may be present in a relatively large proportion of breast cancer patients. Measles virus was associated with younger age at diagnosis, lower tumor grade and overexpression of p53, suggesting that it may play a role in the development of breast cancer.