Early diagnosis improves the survival and success rates of breast cancer treatment. In a study, researchers found that breast milk can be used as a potential tool for early detection of breast cancer.

Researchers from Vall d'Hebron Institute of Oncology (VHIO) in Spain found that breast milk from breast cancer patients diagnosed during pregnancy or postpartum contains circulating tumor DNA that can be detected using liquid biopsy in the future. The findings were published in the journal Cancer Discovery.

The most common symptom of breast cancer is a new lump or mass. Swelling, skin dimpling, nipple pain, nipple discharge and swollen lymph nodes under the arm can also be signs of breast cancer.

However, many women with breast cancer do not experience any symptoms, which can make detection challenging. The American Cancer Society recommends regular breast cancer screening, including breast self-exams, clinical breast exams and mammograms.

During pregnancy and postpartum, breast cells undergo a rapid expansion and hence, the risk of breast cancer is high. However, the diagnoses often occur at an advanced stage in this specific group of women. The team behind the latest study explored the potential of a novel mechanism for early detection.

"During all the years that this unit has been operating, we have observed that breast cancer patients who are diagnosed during pregnancy or, especially, during the postpartum period, have a worse prognosis because they are diagnosed at more advanced stages of the disease," Dr. Cristina Saura, who led the study, said in a news release.

"The physiological changes that occur in the breast during pregnancy and postpartum make tumors more difficult to detect; we have also observed that biologically, postpartum tumors are more aggressive, and women become pregnant at ages when population screening with mammography is not yet carried out," Dr. Saura explained.

The researchers initiated the study in response to a breast cancer patient's concern. She was diagnosed with breast cancer during her third pregnancy and worried that she might have transmitted the tumor to her second daughter through breastfeeding.

Although the researchers knew that tumor cells could not be transmitted to the child through breastfeeding, they decided to analyze the woman's breast milk that she had stored frozen more than a year before the cancer diagnosis.

"When we analyzed the patient's breast milk, we found DNA with the same mutation that was present in her tumor," Dr. Saura said.

They then expanded the study to evaluate breast milk and blood samples from breast cancer patients diagnosed during pregnancy or postpartum and compared them with healthy women who were breastfeeding.

"We analyzed the breast milk and blood samples using two techniques, Next Generation Sequencing (NGS) and Droplet Digital PCR (ddPCR). And we found that there was free circulating DNA of tumor origin in the breast milk. We were able to detect mutations that were present in the tumors of patients with breast cancer in the samples of breast milk of 13 of the 15 patients analyzed. Whereas, in the blood samples collected at the same time, ctDNA was only detected in one of them," study author Dr. Ana Vivancos said.

Although the findings need confirmation through further research, the team believes they will pave the way for the development of noninvasive techniques in the early diagnosis of breast cancer.

"Our results open the door to the future use of breast milk as a new source of liquid biopsy for the early detection of breast cancer in the postpartum period using a non-invasive technique," Dr. Saura said. "We have shown for the first time that breast milk obtained from breast cancer patients contains sufficient ctDNA to be detected by liquid biopsy and that this ctDNA can be detected even before breast cancer can be diagnosed using conventional imaging."

In recent years, researchers have developed liquid biopsy techniques to use blood, urine and saliva for cancer detection. However, liquid blood biopsy is a low-sensitivity tool as it requires a very high amount of circulating tumor DNA for diagnosis.

"So we thought that, because of its proximity to the tumor, breast milk could be an alternative source for detecting the tumor by liquid biopsy," Vivancos said.