Breast cancer can be detected earlier in breast milk than in a mammogram, according to research from the Vall d'Hebron Institute of Oncology (VHIO) that opens the way to improving early detection of the disease in women who have had a son recently.
The breast milk cancer detection test, still experimental, will be tested in women who are over 40 years old when they become pregnant or who have a high risk of breast cancer for hereditary reasons. If the trial results are positive, the technique could begin to be used routinely in the second half of this decade.
“We hope that in the future it can be offered to women of any age who have had a child even if they do not have risk factors,” explains oncologist Cristina Saura, director of the project. “It is a group in which cases of breast cancer are increasing and for which we do not have other early diagnosis options.”
The investigation began following the request of a patient from Vall d'Hebron who was diagnosed with breast cancer in 2017 during her third pregnancy. Concerned that she might have transmitted tumor material to her second daughter while breastfeeding, she asked Dr. Saura to analyze a sample of milk that she still had stored in the freezer.
“We discovered that a genetic mutation of her tumor was already in the milk that had been extracted 18 months before the cancer was diagnosed,” explains Saura, who reassured the patient because “there is no case described in the world in which cancer has been transmitted through breast milk.
That result led the VHIO team to start a study to explore whether breast milk can improve the early detection of breast cancer. The study analyzed the milk of 14 mothers who were diagnosed with breast cancer during pregnancy or shortly after. According to the results now presented in the journal Cancer Discovery, they had an average age of 36 years at the time of diagnosis.
The test developed in the VHIO genomics laboratory, directed by Ana Vivancos, has correctly identified genetic material from tumors in 71% of milk samples extracted from breasts affected by cancer. This test analyzes the 54 most frequently mutated genes in breast cancers of women under 45 years of age.
In the milk extracted from the healthy breasts of the patients, as well as in the milk provided by volunteers without cancer who have contributed to the study, the test result has been negative in all cases.
To perform the test, it is enough to provide ten milliliters of milk from each breast extracted with a breast pump, so “it does not represent any significant discomfort for women,” says Saura. Milk should be expressed at least 14 days after delivery, as it contains little material from the tumor during the first two weeks.
The results obtained so far are not enough to recommend breast milk analyzes for the early detection of cancer, warns Saura. The reason is that it is a retrospective study, in which genetic mutations have been looked for in the milk after the cancer had been diagnosed.
To demonstrate that the test really improves early diagnosis, a prospective study is planned to be carried out soon with 5,000 volunteers who must be healthy at the time of enrolling in the project. The study will focus on pregnant women over 40 years of age, or with hereditary genetic mutations that predispose them to developing breast cancer. It will also include women who have a pregnancy after being diagnosed with cancer, although this is a group in which breastfeeding is not common.
The Vall d'Hebron team plans to collaborate on this prospective study with hospitals throughout Spain, as well as with centers in France, Italy and the United States that have expressed interest in joining the project. The study, which will require a budget of 15 million euros, is in the financing search phase.
In cases where breast milk analysis detects DNA of tumor origin, participants will be recommended to have an ultrasound to confirm the diagnosis. A mammogram will not be recommended as it does not clearly identify tumors during breastfeeding due to the changes that occur in the breast. If the ultrasound is negative, whether another imaging technique is performed and how to follow up each patient will be evaluated on a case-by-case basis.
“Breast cancer is the main cause of death in women between 35 and 45 years old in our environment,” reports Saura. “It usually has a higher risk of metastasis and a worse prognosis when it occurs during pregnancy or in the following years because it is often diagnosed when it is more advanced and due to the biological changes that occur in the breast.”
If the tendency to delay the age of motherhood is taken into account, “it is foreseeable that the number of cases will increase in the coming years,” writes Vall d'Hebron's team in Cancer Discovery. “Breast cancer screening using breast milk could dramatically improve the prognosis and quality of life of diagnosed mothers in the future.”
Until now, the project has had as its main sources of financing the Fero Foundation, the “la Caixa” Foundation, the Carlos III Health Institute, the ISDIN company, the Spanish Society of Medical Oncology, the Spanish Association Against Cancer supported by Lotteries and State Betting, and the solidarity initiative “El Paseíco de la Mama”.
