Basal-like breast cancer represents a distinct molecular subtype accounting for approximately 15–20% of all invasive breast carcinomas. Worth adding: characterified by aggressive clinical behavior, high-grade histology, and limited expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2, this subtype often overlaps clinically with triple-negative breast cancer. Worth adding: within the complex genomic landscape of basal-like disease, focal copy number alterations have emerged as critical markers for risk stratification, therapeutic decision-making, and understanding tumor evolution. Among these, loss of genetic material on the long arm of chromosome 5—designated 5q loss—has garnered particular attention for its recurrent presence and potential functional implications No workaround needed..
Introduction to Basal-Like Breast Cancer Basal-like breast cancer originates from basal epithelial cells of the mammary ductal system and is defined by a specific gene expression profile. Key transcriptional markers include KRT5, KRT17, EGFR, and P63. Unlike luminal subtypes driven primarily by hormonal signaling, basal-like tumors frequently harbor mutations in TP53, a tumor suppressor gene that governs cell cycle arrest and apoptosis. The aggressive nature of this subtype, coupled with the absence of targeted endocrine therapies, underscores the importance of identifying actionable genomic vulnerabilities. Recent large-scale genomic studies have begun mapping the copy number variation (CNV) landscape across basal-like tumors, revealing recurrent patterns that may influence prognosis and response to chemotherapy.
The Concept of Copy Number Alterations in Cancer Genomics Copy number alterations refer to gains or losses of DNA segments, ranging from single exons to entire chromosomes. In cancer, these alterations drive genomic instability, alter dosage of oncogenes and tumor suppressors, and shape the evolutionary trajectory of clones within a tumor. High-throughput platforms such as array comparative genomic hybridization (aCGH), SNP arrays, and whole-genome sequencing have enabled precise mapping of these events. A "loss" denotes deletion of one or more copies of a genomic region, while "gain" indicates amplification. The functional impact of a given CNV depends on the genes encompassed, their regulatory roles, and the cellular context. In basal-like breast cancer, the interplay between point mutations and copy number changes creates a complex mosaic that dictates tumor behavior.
5q Loss: Definition and Genomic Context The 5q region spans approximately 181 million base pairs and contains numerous genes implicated in cell adhesion, signaling, and genomic maintenance. Loss of 5q, often denoted as 5q deletion or 5q-, is a recurrent event in several hematologic and solid malignancies. In the context of basal-like breast cancer, 5q loss is typically focal or arm-level
