BRCA Carriers Show Distinct Protein Signatures in Healthy Breast Tissue, Study Finds

Women who carry mutations in the BRCA1 or BRCA2 genes face some of the highest hereditary risks of breast cancer known to medicine, yet the biological steps that transform their otherwise healthy breast tissue into fertile ground for malignancy have remained frustratingly opaque. Now, a large proteomic study led by researchers at the Mayo Clinic and published in the Journal of Translational Medicine offers one of the most detailed molecular portraits to date of nonmalignant breast tissue from cancer-free mutation carriers. By measuring thousands of proteins across dozens of tissue samples, the team found that the tissue of carriers is not simply a passive backdrop awaiting a second genetic hit. Instead, it displays a coordinated shift in the architecture of its extracellular matrix and basement membrane, the structural scaffolding that surrounds and instructs every cell in the breast.

The study, spearheaded by first authors Nicole Cruz-Reyes, Syed Mohammed Musheer Aalam, and Dowoon Nam under the senior guidance of Derek C. Radisky, Amy C. Degnim, Stacey J. Winham, and Nagarajan Kannan, applied a technique called data-independent acquisition mass spectrometry to 72 nonmalignant breast tissue samples. These specimens came from three groups of women: those without BRCA1/2 mutations who served as controls, cancer-free carriers of BRCA1 or BRCA2 mutations, and carriers who had a prior history of breast cancer. After rigorous quality control, 69 samples and 4,749 individual proteins remained for analysis, a depth of coverage that allowed the researchers to interrogate not just a handful of candidate molecules but the entire detectable protein landscape of the breast.

The analytical strategy was deliberately conservative. The researchers tested differential protein abundance using linear models adjusted for age and for the site or biobank from which the specimens originated, with prespecified checks to guard against spurious associations. When they compared cancer-free carriers against noncarrier controls under this primary model, they identified 435 proteins whose abundance differed at a false discovery rate below 0.10. That number shrank to 49 when the team added an additional adjustment for the year of surgery, a variable that captures shifts in clinical practice and specimen handling over time. The drop is instructive: it shows how much of the apparent molecular difference between groups can be explained by context rather than biology, and it underscores why the authors framed their findings as exploratory rather than definitive.

What survived these statistical gauntlets was a strikingly coherent signal. The most consistent pathway-level finding involved the organization of the extracellular matrix and the basement membrane, including interactions involving laminins, a family of glycoproteins that form a core structural component of the basement membrane; ECM proteoglycans, the sugar-decorated proteins that cushion and signal within the matrix; and non-integrin membrane–ECM interactions, which describe how cells tether to their surroundings through receptors other than the well-known integrins. Notably, the laminin interaction pathway remained enriched at a false discovery rate below 0.10 even in the fully adjusted model that included surgery-year correction, making it the single most robust molecular difference between carrier and noncarrier tissue in the entire dataset.

This emphasis on structural scaffolding is more than a technical curiosity. The extracellular matrix is not merely packing material; it is an active participant in tissue behavior, influencing how cells divide, migrate, differentiate, and respond to stress. Decades of cancer research have shown that stiffened, remodeled, or inflamed matrix environments can promote tumor initiation and progression, and basement membrane integrity is a critical barrier against invasive growth. A systematic shift in matrix and membrane composition in the tissue of BRCA carriers therefore suggests a plausible mechanism by which germline mutations in DNA repair genes could shape the microenvironment long before any tumor appears, potentially lowering the threshold for malignant transformation.

Beyond the matrix program, the study surfaced several secondary, exploratory patterns that add texture to the emerging picture. Carrier tissue showed differences in mitochondrial respiration and in hypoxia and glycolysis pathways, hinting at altered energy metabolism and stress responses. Hemostatic and innate-immune pathways also differed between the groups, suggesting that clotting-related and first-line immune programs may be tuned differently in carrier tissue. Conversely, the researchers observed relative reductions in programs governing intracellular trafficking, proteostasis, the maintenance of proper protein folding and degradation, and mitosis, the machinery of cell division. Each of these observations is exploratory and did not carry the same statistical weight as the matrix findings, but together they sketch a tissue state that is metabolically and immunologically distinct from that of noncarriers.

To make sense of these bulk-tissue measurements, the team turned to context. They compared their protein-level programs against a published single-cell atlas of the human breast, asking which cell types might be responsible for the observed signals. They also annotated their findings against public databases of HLA ligands and T-cell assays, including the Immune Epitope Database and the Cancer Epitope Database and Analysis Resource, to explore whether the proteins altered in carrier tissue might be relevant to immune recognition. These analyses provided contextual annotation rather than proof, but they point toward future experiments: spatial mapping of the matrix program within tissue sections, and direct immunopeptidomics to determine whether any of the altered proteins generate peptide fragments displayed on the cell surface that could be targeted by preventive vaccines or other immunotherapies.

The authors are unusually candid about the limits of their work, and that candor matters for how the findings should be interpreted. Because the surgical indication and specimen context were aligned with the biological group, meaning carriers and controls underwent tissue removal for different clinical reasons, and because quantitative tissue composition was unavailable, the comparison cannot isolate a pure germline BRCA1/2 effect. It also cannot determine the cellular origin of the observed protein changes, establish causality, or predict individual cancer risk. When the team compared cancer-free carriers with carriers who had a history of breast cancer, they found directional concordance in the protein patterns, an observation that is suggestive of a continuum but remains an exploratory comparison in its own right. In short, the study identifies a molecular signature, not a diagnostic test.

Still, the framework the researchers have built is designed to be extended. The work was supported by the Gray Foundation BRCA Prevention Initiative, a program explicitly aimed at reducing cancer risk in mutation carriers before disease develops, and the study’s conclusions position it as a foundation for spatial validation studies, direct HLA immunopeptidomics, and the development of prevention-oriented biomarkers and interventions. For the roughly one in several hundred women who carry pathogenic BRCA1 or BRCA2 mutations, current risk management options range from intensified screening to prophylactic mastectomy, choices that are effective but physically and psychologically demanding. A molecular understanding of what makes carrier tissue permissive to cancer could eventually open a middle path: surveillance or interventions aimed at the earliest biological deviations rather than the end-stage disease.

The study also exemplifies a broader shift in how hereditary cancer risk is being studied. Rather than focusing exclusively on the tumor or on the mutated gene itself, researchers are increasingly profiling the apparently normal tissue that surrounds future cancers, treating it as a landscape shaped by germline genetics, hormonal history, immune activity, and structural remodeling. Mass spectrometry at this scale, resolving nearly five thousand proteins across dozens of carefully matched specimens, was impractical a decade ago, and the integration of such data with single-cell atlases and immune epitope resources reflects a maturing computational ecosystem. The Mayo Clinic team’s finding that basement membrane and extracellular matrix organization stands out as the most durable difference in cancer-free BRCA carriers gives prevention researchers a concrete molecular thread to pull. Whether that thread leads to actionable biomarkers or preventive strategies will depend on the validation studies the authors themselves call for, but the message of the work is clear: the breast tissue of BRCA mutation carriers is already telling a molecular story long before cancer arrives, and scientists are finally learning to read it.

Subject of Research: Proteomic differences in nonmalignant breast tissue of cancer-free BRCA1/2 mutation carriers

Article Title: Global proteomic comparison highlights an extracellular-matrix and basement-membrane program in nonmalignant breast tissue from cancer-free BRCA1/2 carriers

Article References: Cruz-Reyes, N., Musheer Aalam, S. M., Nam, D., Mun, D.-G., McCauley, B. M., Hoskin, T., Mangalaparthi, K. K., Arokia Balaya, R. D., Pacheco-Spann, L., Asmann, Y., Jessen, E., Knutson, K. L., Sherman, M. E., Pandey, A., Kannan, N., Degnim, A. C., Winham, S. J., & Radisky, D. C. (2026). Global proteomic comparison highlights an extracellular-matrix and basement-membrane program in nonmalignant breast tissue from cancer-free BRCA1/2 carriers. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09067-0

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09067-0

Keywords: BRCA1, BRCA2, breast cancer, proteomics, extracellular matrix, basement membrane, laminin, mass spectrometry, cancer prevention, innate immunity, Mayo Clinic, molecular pathology