Breast cancer involves cell changes in the body, but new research shows some changes linked to the disease may actually be found in healthy breast tissue, as well. The findings could have implications for diagnosis and what we know about the genetic origins of the disease.

Researchers at the University of Texas MD Anderson Cancer Center recently studied more than 83,000 epithelial breast tissue cells from 49 breast cancer-free women undergoing breast reduction surgery. Epithelial cells are found throughout our bodies and can serve as barriers or protectors of organs. The team was looking specifically for aneuploid epithelial cells, which have chromosomal abnormalities and are common in breast cancer. To detect them, the researchers looked at chromosomal copy number changes in the tissue.

According to their findings, published in the journal Nature, all the women had such cells, despite being cancer-free.

Dr. Nicholas Navin, lead investigator and chair of Systems Biology at the cancer center, says. “A cancer researcher or oncologist seeing the genomic picture of these normal breast tissue cells would classify them as invasive breast cancer. We’ve always been taught that normal cells have 23 pairs of chromosomes, but that appears to be inaccurate because every healthy woman that we analyzed in our study had irregularities, bringing up the very provocative question about when cancer actually occurs.”

In all, the participants’ samples had a median of 3.19% aneuploid epithelial cells, which expanded and increased with age. Additionally, nearly 83% of these cells underwent clonal expansion, changing in ways similar to invasive breast cancers. They also displayed two different lineages, some with copy number changes similar to estrogen receptor-positive breast cancer and some with changes similar to estrogen receptor-negative breast cancer, suggesting they have different origins.

The team says the findings may call into question how breast cancer originates genetically and how these cells may impact false positives. Because epithelial cells are found throughout the body, this could also have implications for cancers of other organs.

However, more research is needed.

Dr. Navin says, “It just shows that our bodies are imperfect in some ways, and we can generate these types of cells over our lifetime. This has pretty big implications not just for the field of breast cancer, but potentially for multiple cancer types. This doesn’t necessarily mean that everyone is walking around with precancer, but we need to think about ways to set up larger studies to understand the implications for developing cancer.”