Triple-negative breast cancer (TNBC) is recognized as one of the more aggressive and challenging breast cancers to treat. Lacking the three standard hormonal markers associated with estrogen receptors, progesterone receptors, and HER2, this absence complicates the selection of effective treatment strategies for healthcare providers.
Researchers characterize TNBC as a collection of various diseases with distinct molecular characteristics that impact how the cancer manifests and its response to treatments. They utilize specific genes and gene products to categorize TNBC types. It is important to note that there are overlaps in the current classifications, which might be explained by the presence and levels of particular chemical molecules on the DNA. These molecules play a role in regulating whether genes are activated or deactivated in cells through processes known as DNA methylation.
In this study, researchers from Sweden explored how the distribution and patterns of DNA methylation delineate different forms of TNBC, influencing tumor behavior and interactions with the body’s immune system and its treatment responses. They analyzed 235 tumor samples from various patients in Sweden, ensuring that the data was refined to focus solely on cancerous cells rather than healthy tissue.
Employing a statistical technique known as Non-negative matrix factorization, they identified two primary categories of TNBC based on DNA methylation patterns: basal and nonbasal groups. This categorization aligns with previous classifications grounded in how cells interpret gene functions, termed gene expression. The basal group comprised tumors that were typically more active in immune responses and had a higher incidence of mutations linked to DNA repair issues, notably involving the common BRCA1 gene. Conversely, although the nonbasal group lacked hormone receptors, they exhibited increased activity in genes that influence hormonal responses.
Utilizing statistical assessments, the researchers subdivided each major group into smaller subtypes. Within the basal tumors, they identified three subgroups, referred to as basal1, basal2, and basal3, characterized by varying levels of immune cell activity and gene expression profiles. One specific subgroup, Basal3, demonstrated elevated expression of proteins that aid tumors in evading the immune system. The researchers found that specific DNA methylation patterns could activate or deactivate these proteins, indicating that patients with basal tumors might benefit from existing cancer treatments targeting this protein. The Basal2 subgroup expressed genes that inhibit immune activity, while the Basal1 subgroup displayed no significant immune-related behavior.
In the nonbasal category, researchers distinguished two subtypes: nonbasal1 and nonbasal2. Both of these subgroups were more prevalent among older patients and exhibited lower survival rates compared to the basal subgroup. The Nonbasal2 group encompassed tumors that influenced hormonal activity and responses to fatty treatments, whereas the Nonbasal1 group experienced more frequent disruptions in genes associated with tumor suppression.
Across all groups, researchers identified numerous genes whose methylation could modulate tumor growth and responses to the surrounding environment. To validate their findings in a broader context, they sourced independent tumor datasets from global databases and conducted similar classification analyses. They confirmed that the identified methylation subtypes appeared in other TNBC samples and correlated methylation patterns with tumor defense mechanisms, pinpointing strategies TNBC tumors may utilize to evade the immune system.
The researchers also acknowledged several limitations of their study. Their focus on DNA methylation represents just one of many chemical modifications that can influence TNBC behavior. Some of the independent datasets utilized originated from general breast cancer studies and were not exclusively focused on TNBC. Additionally, a significant portion of the data came from Western and Northern European populations, which may limit the applicability of the findings to individuals from other ethnicities. They emphasized the necessity for larger and more diverse datasets to gain a comprehensive understanding of TNBC subtypes.
In conclusion, the researchers posited that examining DNA methylation in patient samples could effectively categorize TNBC into meaningful subtypes, each with unique biological features, immune environments, and potential treatment responses. They recommended that future studies explore the origins of epigenetic modifications, such as DNA methylation, and how these alterations contribute to variations in TNBC subtypes.
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Source: sciworthy.com
