Title : Molecular-genetic study of low-grade and high-grade “basal-like” (triple-negative) breast carcinomas
Abstract:
Introduction: Basal-like breast carcinomas are immunohistochemically positive for basal-type keratins such as K 5/6, K14, and K17 and mostly are triple-negative (negativity for ER, PR, and Her2/neu). “Basal-like” or triple-negative breast carcinoma is mostly known as a distinct clinicopathologic entity with aggressive clinical behavior. Therefore, most patients with this type of breast carcinoma are treated with chemotherapy. There are, however, a number of rare examples of BLC/TNC such as adenoid-cystic carcinoma (ACC), fibromatosis-like carcinoma (FLC), secretory carcinoma (SC), etc., that are associated with low-grade atypia, low mitotic activity and good prognosis. The aim of our study was to compare several example of high-grade BLC/TNC with rare variant of low-grade BLC/TNC by means of Next Generation Sequencing and Copy Number Variation (CNV)-Assay.
Material and Methods: Thirty cases of BLC/TNC (15 low-grade and 15 high-grade) were examined. For mutational analysis, we used NGS performed by FoundationOne (Foundation Medicine Inc. Cambridge, MA, USA) with a NGS panel of 322 genes. We also used OncoScan (Thermo Fisher Scientific, Walham, MA, USA) in order to evaluate CNVs and loss of heterozygosity (LOH) of the whole genome. All molecular-genetic analyses were performed on formalin-fixed, paraffin-embedded material.
Results: Low-grade and high-grade BLC/TNC are molecular-genetically drastically different with regard to Mutations and CNVs. The NGS analysis revealed significantly higher tumor mutation burden in high-grade (TMB: 95% CI: 44.51 – 79, 48) compared to TMB of the low-grade group (TMB: 95% CI: 20, 96 – 35, 03). The difference of TMB in both groups were highly significant (p = 8.5x 10-3). High-grade BLC/TNC showed almost always (93.33%) TP53 mutations, while not a single case of low-grade BLC/TNC revealed TP53 mutations. While multiple amplifications of oncogenes were identified in the high-grade group, amplification of oncogenes could hardly be observed in the low-grade group.
The CNV Assay revealed much higher number and larger changes (gains and losses) in the high-grade group as compared to those identified in the low-grade group. The percentage of genome change (combination of CNVs and LOH) was significantly different in the two groups (p = 8.63x 10-6, 95% CI : 1.21% - 5.46% in the low-grade group and 37,21% - 60,43% in the high-grade group).
Conclusion: Basal-like or triple negative breast carcinomas do not represent a homogenous entity. The oncologists needs to recognize the rare low-grade BLC/TNC of the breast, which are morphologically, molecular-genetically, and clinically drastically different from the more common and high-grade BLC/TNC. The distinction between the two groups has a major impact on the therapeutic management of the patients, particularly with regard to the chemotherapy.
