Clinical Implications of p16 Evaluation in a Purposively Sampled Cohort of High-Risk Breast Cancer Phenotypes

The overexpression of cyclin-dependent kinase inhibitor p16 (INK4a) is widely recognized as a surrogate marker for high-risk human papillomavirus (HPV) in anogenital malignancies, but its significance in invasive breast carcinoma is complex and remains frequently debated. While historically investigated as a viral proxy, emerging evidence suggests that elevated p16 levels in breast tissue may instead reflect intrinsic cell-cycle dysregulation and retinoblastoma (Rb) pathway disruption, though direct molecular confirmation is lacking in this area of research. This study aims to evaluate the role of p16 as an indicator of tumor aggressiveness for high-risk phenotypes. We conducted a retrospective study of 100 female patients with invasive breast carcinoma. Employing a purposive sampling strategy rather than a consecutive series, we analyzed a targeted cohort consisting predominantly of triple-negative breast cancer (TNBC) and high-grade tumors to evaluate biomarker patterns specifically in advanced disease contexts. Immunohistochemical assessment was performed using a standardized cumulative nuclear and cytoplasmic scoring system, with expression thresholds defined by receiver operating characteristic (ROC) curve analysis optimized for histological grade. p16 overexpression was a predominant characteristic of these aggressive tumors and was identified in 68% of cases. Statistical evaluation revealed a robust and significant correlation between p16 overexpression and the triple-negative molecular subtype, as well as a marked inverse relationship with estrogen receptor (ER) status. Although p16 levels were frequently associated with specific aggressive phenotypes, no statistically significant difference in overall survival was observed between expression groups, a finding attributable to the uniformly high-risk nature of the selected cohort. This study suggests an association between p16 expression levels and aggressive tumor features, although the study design limits causal inferences. A non-significant trend towards p16 overexpression was observed in ductal carcinomas compared to lobular subtypes, while high p16 expression was noted exclusively in G3 tumors within this selected cohort, a finding influenced by the purposive sampling strategy and the ROC-based cutoff definition. Tumor necrosis was more prevalent in p16-overexpressing tumors. Furthermore, p16 levels showed a strong inverse relationship with estrogen receptor (ER) status, as they were significantly elevated in ER-negative and triple-negative tumors compared to luminal phenotypes.