Background: Breast cancer is the most prevalent and second leading cause of cancer-related death in women worldwide. Despite early detection and better treatment therapies, 30% of early-stage breast cancer patients still develop recurrent disease. Breast cancer is a heterogeneous disease comprising several molecular subtypes, commonly classified into clinical subtypes based on the hormone receptor status. These subtypes included luminal A and luminal B, which have different prognoses. Breast cancer development and progression involve many factors. Polymorphisms of PD-1, PD-L1, and PD-L2 genes have been previously associated with high risk and prognosis of cancer. However, no studies have associated PD-1, PD-L1, and PD-L2 polymorphisms with primary breast cancer subtypes. Hence, this study evaluated functional single nucleotide polymorphisms of PD-1, PD-L1, and PD-L2 with primary breast cancer subtypes, luminal A, and luminal B. In addition, we evaluated the PD-L1 protein expression in relation to primary breast cancer subtypes and stages. Results: There were no significant differences in the allele frequencies of PD-1 polymorphisms (rs2227981 G>A, rs7421861 A>G, and rs11568821 C>T) and PD-L1 polymorphisms (rs10815225 C>T and rs2282055 T>G) when compared with the general European population. However, a significant difference was detected in one of the PD-L2 polymorphisms (rs1009759 A>G), with the G allele higher in breast cancer patients than in the general European population. A higher prevalence of the T allele of PD-L1 polymorphism rs2282055 T>G was observed in luminal B breast cancer patients compared with luminal A. No significant difference was detected in other polymorphisms. We also observed that the PD-L1 rs2282055 TT genotype was more prevalent in luminal B breast cancer patients compared with luminal A. Our results found no association of the selected SNPs in the PDCD1 gene with breast cancer risk. Similarly, the protein expression data showed that PD-L1 and PD-L2 are associated with an aggressive phenotype, Luminal B, and advanced breast cancer stage. Conclusion: These findings suggest that immune checkpoint polymorphisms are associated with the risk and subtypes of breast cancer.

Background/Objectives Ki‑67 is widely used as an immunohistochemical marker of tumor proliferation in hormone receptor–positive (HR‑positive), HER2‑negative breast cancer, but its inter-pretation is limited by variability and uncertain concordance with genomic assays. The Oncotype DX® Recurrence Score (RS) is a validated multigene assay with established prognostic and predictive utility. This study evaluated the relationship between Ki‑67 and RS in clinical practice. Methods We retrospectively analyzed women in Greece with early‑stage estrogen receptor–positive, HER2‑negative breast cancer without distant metastasis (pM0) who under-went Oncotype DX testing between 2020 and 2023. Eligible patients were node nega-tive or postmenopausal with node positive disease. RS was categorized as low (0–25) or high (>25). Ki‑67 was assessed using binary (< 20% vs ≥20%) and three‑tier (≤5%, >5%–< 30%, ≥30%) classifications. Associations were analyzed using correlation, con-cordance, and nonparametric methods. Results Among 2,967 patients, the median RS was 16, with similar distributions across nodal subgroups. Ki‑67 and RS demonstrated a moderate positive correlation as continuous variables (r = 0.42, p < 0.001). After stratification, associations with RS were observed only in tumors with high Ki‑67 expression, whereas no correlation was detected in low or intermediate groups. RS distributions differed significantly across Ki‑67 strata. Overall concordance between Ki‑67‑based proliferation categories and RS‑based ge-nomic risk was 56.2%, with discordant cases in both directions. Conclusions Ki‑67 shows a moderate association with Oncotype DX RS, but substantial discordance indicates it should not substitute genomic testing in HR‑positive/HER2‑negative early breast cancer.

Background/Objectives: Ki-67 is widely used as an immunohistochemical marker of tumor proliferation in hormone receptor-positive (HR-positive), HER2-negative breast cancer, but its interpretation is limited by variability and uncertain concordance with genomic assays. The Oncotype DX^® Recurrence Score (RS) is a validated multigene assay with established prognostic and predictive utility. This study evaluated the relationship between Ki-67 and RS in clinical practice. Methods: We retrospectively analyzed women in Greece with early-stage estrogen receptor-positive, HER2-negative breast cancer without distant metastasis (pM0) who underwent Oncotype DX testing between 2020 and 2023. Eligible patients were node-negative or postmenopausal with node-positive disease. RS was categorized as low (0–25) or high (>25). Ki-67 was assessed using binary (5–<30%, ≥30%) classifications. Associations were analyzed using correlation, concordance, and non-parametric methods. Results: Among 2967 patients, the median RS was 16, with similar distributions across nodal subgroups. Ki-67 and RS demonstrated a modest positive correlation as continuous variables (R = 0.30, p < 0.001). After stratification, associations with RS were observed only in tumors with high Ki-67 expression, whereas no correlation was detected in low or intermediate groups. RS distributions differed significantly across Ki-67 strata. Overall concordance between Ki-67-based proliferation categories and RS-based genomic risk was 56.2%, with discordant cases in both directions. Conclusions: Ki-67 shows a modest association with Oncotype DX RS, but substantial discordance indicates Ki-67 should not substitute genomic testing in HR-positive/HER2-negative early breast cancer.

In breast cancer, current knowledge of the associations between clinicopathologic characteristics, genetic changes, and subtype-specific patterns remain unclear. This research investigated how pathological and clinical variables affect the actionability of NGS-based tumor molecular data. Materials and methods: 227 breast cancer patients referred to Genekor’s laboratory for tumor molecular profile analysis were included in the study. Pathology records, available in all cases, were used to assess critical clinicopathological features including HER2, ER, PR, Ki67, grade, metastatic site, and age. A 1021 gene NGS-based multigene panel was utilized to assess tumors’ biology alongside tumor mutational burden (TMB) and microsatellite instability (MSI) Results: Comprehensive genomic profiling revealed that 95.6% of the patients harbored at least one oncogenic or likely oncogenic alteration, highlighting the high diagnostic yield of NGS-based testing. Distinct subtype-specific patterns were observed: HR+/HER2-tumors were enriched for PIK3CA and ESR1 gene alterations, while Triple Negative Breast Cancer (TNBC) was dominated by TP53 alterations. Clinically actionable alterations were most common in HR+/HER2-tumors (~60% on-label), whereas TNBC more often harbored off-label or trial-associated targets. The inclusion of tumor-agnostic biomarkers (TMB/MSI) increased on-label actionability up to 64.5% in ER−/PR+ tumors. primarily driven by TMB-high cases. Median TMB values were low, and age was the only independent predictor. Furthermore, the presence of actionable alterations was significantly higher in metastatic tumors, and TP53 alterations were associated with aggressive tumor characteristics.Conclusions: Comprehensive NGS-based genomic profiling identifies clinically actionable alterations in over half of breast cancer patients, with substantial variability across molecular subtypes. The HR+/HER2-subtype demonstrates the highest prevalence of on-label actionable biomarkers. These findings support the routine implementation of comprehensive genomic profiling, especially in metastatic HER2-negative breast cancer, to guide precision oncology strategies and enable enrollment in biomarker-driven clinical trials.