Cross-ancestry proteome-wide Mendelian randomization of plasma proteins and breast cancer susceptibility
This study utilizes cross-ancestry Mendelian randomization to identify and prioritize twelve circulating plasma proteins, including three with the strongest cumulative evidence (LRRC25, PARK7, and LRRC37A2), as causal candidates for breast cancer susceptibility, thereby highlighting actionable biological pathways while emphasizing the need for more diverse proteomic resources.
Original paper dedicated to the public domain under CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Breast cancer is not a single disease but a collection of related conditions, each driven by different biological mechanisms. For decades, scientists have mapped the genetic code of people who develop the disease, finding hundreds of locations in our DNA that influence risk. However, most of these genetic clues sit in regions that do not code for proteins, leaving researchers with a puzzle: they know a specific genetic variant increases risk, but they do not know which protein or biological pathway is actually doing the work. To solve this, scientists look at the proteome, the vast collection of proteins circulating in our blood. These proteins act as messengers and workers, translating the static instructions of our genes into the dynamic processes of life. Because proteins are closer to the actual disease process than genes are, and because they can often be targeted by medicines, identifying which specific proteins drive breast cancer risk is a crucial step toward better prevention and treatment.
A team of researchers recently tackled this challenge by using a method called Mendelian randomization. This approach treats genetic variants as natural experiments. Since a person's genes are fixed at conception and cannot be changed by their lifestyle or environment, they serve as reliable markers. If a genetic variant is known to raise the level of a specific protein, and that same variant is also found more often in people with breast cancer, it suggests that the protein itself plays a causal role in the disease. The researchers applied this logic on a massive scale, examining nearly two thousand different proteins in the blood. They combined data from over 156,000 women with breast cancer and more than 200,000 without it, drawing from populations of European, East Asian, and African ancestry to ensure the findings applied broadly.
The study identified twelve specific proteins in the blood that appear to influence the likelihood of developing breast cancer. For eight of these proteins, the findings confirmed what previous, smaller studies had hinted at. However, the research also highlighted four new candidates that had not been previously prioritized as major players in breast cancer risk. The team found that higher levels of five of these proteins were linked to an increased risk of the disease, while higher levels of the other seven were linked to a reduced risk. This distinction is vital because it points toward different biological pathways: some proteins might be fueling the disease, while others might be part of the body's natural defense system.
To ensure these results were not flukes, the researchers subjected them to a rigorous series of checks. They looked to see if the genetic signals for the proteins and the disease came from the same spot on the DNA, which would strongly suggest a direct link. They also tested the findings in independent groups of people from Iceland and Japan, and in a diverse group of participants from the "All of Us" research program in the United States. The results were not uniform across all checks, which is common in complex biology, but three proteins stood out with the strongest cumulative support: LRRC25, PARK7, and LRRC37A2. These three showed consistent signals across the different types of analysis, suggesting they are likely genuine contributors to breast cancer susceptibility.
The study also revealed that the role of these proteins can vary depending on the specific type of breast cancer and the ancestry of the person. For instance, one protein called DNPH1 showed a confusing pattern: it appeared to increase risk in people of European ancestry but seemed to decrease risk in people of East Asian ancestry. This discrepancy highlights a major limitation in current research: most genetic data comes from people of European descent, and the tools used to predict protein levels in other groups are not yet perfect. Similarly, when the researchers looked at different subtypes of breast cancer, they found that some proteins were most strongly linked to aggressive forms of the disease, while others were tied to slower-growing types. This suggests that a single protein might play different roles in different contexts, or that the disease mechanisms are more varied than previously thought.
Ultimately, this research provides a genetically informed list of targets for future investigation. It moves beyond simple association to suggest which proteins are likely to be causal agents in breast cancer. While the study does not offer a new treatment or a diagnostic test for patients today, it narrows the field for scientists. By pinpointing these twelve proteins, particularly the three with the strongest evidence, the study offers a roadmap for the next generation of research. The goal now is to understand exactly how these proteins function in the body and whether they can be safely manipulated to prevent the disease or stop it from growing. The findings underscore the need for more diverse genetic data to ensure that future medical breakthroughs benefit everyone, regardless of their background.
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