Breast Milk Liquid Biopsy for Early-Stage Breast Cancer Detection

Carla Nieto Martínez

November 17, 2023

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, Spain.

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 (ctDNA) that can be detected by a liquid biopsy of the milk.

Saura explained to Medscape's Spanish edition 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 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 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 Vivancos, the sensitivity of this panel exceeds 70%. This means that for all the patient samples analyzed using this panel, seven 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. Therefore, using this panel for early detection of this type of tumor during lactation should contribute to addressing a medical need that, until today, has gone unmet," noted Vivancos.

As for this unresolved need, 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."

More Direct Contact With Tumor Cells

In Saura's opinion, in Spain, just like taking a small blood sample from newborns in a heel-prick test to rule out metabolic diseases, milk samples could be taken from women who give birth to rule out or diagnose breast cancer.

As to the potential advantages that breast milk liquid biopsy could have over similar techniques like blood liquid biopsy, Vivancos pointed to the results of her study: "We have seen that breast milk liquid biopsy was positive for the presence of circulating tumor DNA in 87% of cases, whereas blood only revealed the presence of this marker in 8% of cases. This difference indicates that breast milk is a biofluid that is in more direct contact with tumor cells and therefore will be more informative in earlier stages."

Saura explained that the data does not lie when it comes to these tumors in pregnant or postpartum women. "In general, they tend to have a worse prognosis because, in most cases, they are diagnosed in advanced stages. Furthermore, it is typically assumed that the physiological changes in the breasts during gestation and lactation, which are considered to be normal, may hide a developing tumor. The fact is that postpartum breast cancer, understood to be the 10 years after delivery, accounts for 40% to 45% of breast cancer cases diagnosed before age 45."

The researchers plan to continue this project. "Our next step to confirm the usefulness of breast milk as a new tool for liquid biopsy for early detection of breast cancer during the postpartum period is to perform this noninvasive test in thousands of women," said Saura.

Goal: Standardize the Test as a Screening Method

"Based on the results we've published, we're starting a study aimed at collecting breast milk samples from 5000 healthy women around the world who became pregnant at age 40 or older, or who got pregnant at any age and carry mutations that increase their risk of breast cancer," she added.

When asked when they expect to have preliminary results from this new study, Saura stated that it's not yet possible to say exactly when. "We're still waiting for funding to continue this project, but we continue performing analyses on a case-by-case basis. Of course, if we detect any abnormalities in these women, we will follow the established protocol to confirm diagnosis and start treatment if necessary."

When asked whether it is reasonable to expect breast milk liquid biopsy to become normalized as a screening method for women of childbearing age who have a history or risk factors for developing breast cancer, Vivancos said, "That's the scenario we see in the future and what we wish to contribute toward by providing scientific evidence to make it a reality."

"For now, our goal is to validate whether circulating tumor DNA can be detected by breast milk liquid biopsy even before breast cancer can be diagnosed using conventional imaging techniques. If we can validate these preliminary results, we will be able to detect breast cancer early using a noninvasive test like breast milk liquid biopsy," explained Saura.

Lastly, and in view of the issues that are still unresolved when it comes to the detection and treatment of breast cancer during pregnancy, Saura highlighted the emotional impact that a diagnosis of pregnancy-related cancer has on women and on those close to them. "But the first thing they need to know is that diagnosis is not necessarily synonymous with termination of the pregnancy. On the contrary, this tumor can be treated during pregnancy, since surgery can be performed at any time, and chemotherapy can be started in the second trimester. Proof of this is the 72 children who have been born under these circumstances in the past 20 years at the Vall d'Hebrón University Hospital. This hospital is a pioneer in Spain thanks to its multidisciplinary program for education and specific follow-up with women who have been diagnosed with a breast tumor during pregnancy."

Saura and Vivancos report no relevant financial relationships.

This article was translated from the Medscape Spanish edition.


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