Breast cancer has a worse prognosis when diagnosed during pregnancy or postpartum. Methods for early detection are needed, as evidenced every day in the multidisciplinary unit for treating pregnancy-associated breast cancer, which operates within the breast unit at the Vall d’Hebron University Hospital in Barcelona.
The team working in this field is led by Cristina Saura, PhD, who is also head of the Breast Cancer Group at the Vall d’Hebron Institute of Oncology (VHIO). The results of a study recently published in Cancer Discovery show, for the first time, that breast milk from breast cancer patients contains circulating tumor DNA that can be detected by a liquid biopsy of the milk.
Dr. Saura explained in an interview why they began to pursue this research, which, in one sense, fell into their laps. “In this case, it arose from the concerns of a breast cancer patient who was diagnosed while pregnant with her third daughter. She was actually the one who came up with the idea for the project. She was worried that she had transmitted the tumor through her breast milk to her second daughter while breastfeeding. She had been breastfeeding for a long time and had stretched it out until shortly before she was diagnosed with breast cancer. So she brought us a sample of breast milk that she had stored in her freezer.
“So, thanks to her, that’s where our project started. Though we knew that breast cancer is not transmitted through breast milk, we decided to test the sample and look for markers that could help our research. In the end, when we analyzed the patient’s breast milk, we found DNA with the same mutation that was present in her tumor,” explained Dr. Saura. She noted that the breast milk they analyzed had been frozen for more than a year before the patient’s cancer diagnosis.
In terms of methodology, Ana Vivancos, PhD, head of the VHIO cancer genomics group and also one of the authors of the study, explained that they used two techniques to analyze the breast milk and blood samples: next-generation sequencing and droplet digital polymerase chain reaction. These methods confirmed the presence of ctDNA in the breast milk.
High-sensitivity genomic panel
“We were able to detect tumor mutations in milk samples from 13 of the 15 patients with breast cancer who were tested, while circulating tumor DNA was detected in only one of all the blood samples that were collected at the same time,” said Dr. Vivancos. “The samples from the two patients for whom no mutation was detected were discovered to be colostrum that had been collected during the first few hours of lactation.”
As a next step to make this finding practically useful, the research team designed a genomic panel using next-generation sequencing as a potential method for early detection of breast cancer. “We’ve developed a panel that uses hybrid capture chemistry and unique molecular identifiers that ensure better sensitivity during next-generation sequencing. The panel has been calibrated, based on the existing literature, to detect the genes that are most frequently mutated in breast cancer in young women under 45 years old.”
According to Dr. Vivancos, the sensitivity of this panel exceeds 70%. This means that for all the patient samples analyzed using this panel, 7 out of 10 cases are detected with 100% specificity.
“In practice, the panel design allows us to detect mutations in more than 95% of breast cancer cases in women under 45 years old. noted Dr. Vivancos.
As for this unresolved need, Dr. Saura explained that there is currently no system or tool available to allow early suspicion of breast tumors in pregnant women prior to diagnosis. “That’s exactly the goal of this research: to screen for breast cancer in women who have just given birth. Now, it needs to be validated in a larger group of women in a clinical trial.”