Milk-Producing Protein Speeds Spread of Breast Cancer Cells to Lungs

Researchers in Australia have identified a milk-producing protein in a breast model of postpartum women that speeds up the spread of some breast cancer cells. According to the research first published in PLoS Biology, there is a link between a protein essential for milk production and an increased risk of breast cancer metasasis.

The protein, called ELF5, is a transcription factor that switches on targeted genes in response to certain signals. ELF5 causes immune cells to gather in breast tumors, which spread to the lungs. In a model of breast cancer, this caused inflammation and encouraged new blood vessels to form around the tumor. These new blood vessels became “leaky,” which created an opportunity for cancer cells to escape into the blood and spread to the lungs.

This surprising news comes at a time when previous research has demonstrated how pregnancy and breastfeeding can have a protective effect against some breast cancers. However, this new finding appears to be related only to one type of breast cancer-luminal A.

The luminal types of breast cancer are estrogen receptor (ER)–positive. Luminal A breast cancers are low grade, tend to grow slow, and have a good prognosis.

During pregnancy, ELF5 is active in cells within the breast, switching on the genes that drive them to become milk-producing cells during lactation. When those cells turn into cancer cells, ELF5 is active in the role of cancer progression, leading to aggressive forms of breast cancer that have a poor prognosis.

“We show that ELF5 drives the spread of breast cancer to the lungs in a model of breast cancer – and it also predicts early metastasis in patients with luminal A breast cancer,” said David Gallego-Ortega, PhD, of Sydney’s Garvan Institute of Medical Research, in a news release.

The researchers went on to show that, in samples from patients with luminal breast cancer, high ELF5 levels were seen in the cancers of patients whose disease worsened rapidly. This suggests that ELF5 levels could be used in the future to identify patients who might benefit from treatments usually used in other types of cancer.

The findings point the research science community in new directions for developing new therapies. Specifically, therapies that regulate innate parts of the immune system, such as anti-inflammatory drugs, may lead to possible treatment options for luminal breast cancers, according to Dr. Gallego-Ortega.