Opposite effects of microchimerism on breast and colon cancer

Detection of Y chromosome, thought to originate from previous pregnancies with a male fetus, is common in women. Lower concentrations have been reported in women with breast cancer than cancer-free women. Data in women with other types of cancer are sparse. The purpose of the study was to determine whether the lower concentrations predate cancer diagnosis, and whether a possible beneficial effect was specific to breast cancer.

We conducted a prospective case-cohort study of 50-64-year-old Danish women enrolled in the diet, cancer and health cohort. Blood samples and questionnaire data were obtained during 1993-1997 when all women were cancer-free. In 2006 all women were followed up for incident breast and colon cancer in national registers. In blinded analyses, we analysed buffy coat DNA for Y chromosome (DYS14) as a marker of male microchimerism.

We detected male microchimerism in 70% of 272 cancer-free women, 40% of 89 women who later developed breast cancer, and 90% of 67 women who later developed colon cancer. The corresponding odds ratios were 0.30 (95% confidence interval (CI) 0.17-0.52) for breast, and 3.9 (95%CI 1.6-9.5) for colon cancer.

Detection of male microchimerism was strongly associated with reduced risk of developing breast cancer and also the increased risk of developing colon cancer. Confirmatory findings based on an improved study design, failure to identify important confounders and the strength of the associations lead us to believe that microchimerism may be highly relevant to later cancer development. However, the present study does not allow us to identify the underlying biological mechanisms.