Abstract SP112: Spatial variance signatures/Intra-tumor zonation in TNBC

It is increasingly clear that triple negative breast cancer (TNBC) is a heterogeneous disease with variable clinical presentation, histological features and response to therapy. While these differences have been partially explained by inter- and intra-tumoral heterogeneity, spatial heterogeneity represented by the tumor architecture plays a critical role in clonal evolution and displays a landscape for different compartment-specific processes and cell-to-cell specific interactions. To better understand the impact of spatial heterogeneity on gene-expression-defined cell populations, we have coupled single-cell RNA sequencing with multiplex immunofluorescence (IF). Multiplex immunofluorescence using specific markers for each cell cluster, integrated with computational image analyses and neighborhood maps, has revealed spatial zonation of single cell subpopulations. Zonation of single cell populations was coupled to hypoxia and overlayed distinct metabolic tumor zones and defined areas of differential stress and cell plasticity that give rise to tumor cells with enhanced fitness and aggressivity.

Citation Format: M Park, C Martínez Ramirez, Y Yang, A Blanchet-Cohen, H Kuasne, A Fortier, J Ragoussis, P Savage, A Omeroglou, S Meterissian, S Costantino, C Kleinman. Spatial variance signatures/Intra-tumor zonation in TNBC [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SP112.

DNA methylation patterns of candidate genes regulated by thymine DNA glycosylase in patients with TP53 germline mutations

Li-Fraumeni syndrome (LFS) is a rare, autosomal dominant, hereditary cancer predisposition disorder. In Brazil, the p.R337H TP53 founder mutation causes the variant form of LFS, Li-Fraumeni-like syndrome. The occurrence of cancer and age of disease onset are known to vary, even in patients carrying the same mutation, and several mechanisms such as genetic and epigenetic alterations may be involved in this variability. However, the extent of involvement of such events has not been clarified. It is well established that p53 regulates several pathways, including the thymine DNA glycosylase (TDG) pathway, which regulates the DNA methylation of several genes. This study aimed to identify the DNA methylation pattern of genes potentially related to the TDG pathway (CDKN2A, FOXA1, HOXD8, OCT4, SOX2, and SOX17) in 30 patients with germline TP53 mutations, 10 patients with wild-type TP53, and 10 healthy individuals. We also evaluated TDG expression in patients with adrenocortical tumors (ADR) with and without the p.R337H TP53 mutation. Gene methylation patterns of peripheral blood DNA samples assessed by pyrosequencing revealed no significant differences between the three groups. However, increased TDG expression was observed by quantitative reverse transcription PCR in p.R337H carriers with ADR. Considering the rarity of this phenotype and the relevance of these findings, further studies using a larger sample set are necessary to confirm our results.

Base excision repair genes XRCC1 and APEX1 and the risk for prostate cancer

Prostate cancer is the second cause of cancer death in Brazilian men. One of the relevant phenomena to the inherited susceptibility is the presence of allelic variants in genes involved with the DNA repair pathway. The aim of this study was to analyze the frequencies of prevalent, heterozygous and rare genotypes of the base excision repair genes APEX1 and XRCC1 in a case-control study and relate the genotypes with tumoral aggressiveness. DNA from peripheral blood of 172 patients and 172 controls were analyzed by RFLP-PCR method. The polymorphisms were also evaluated in relation to clinical and pathological parameters. The OR (Odds Ratio) and confidence interval (CI = 95%) were used in the association study and the Chi-square and ANOVA tests for the evaluation of histopathological parameters. The rare genotypes frequencies of the gene APEX1 increased the risk for the development of prostate cancer (OR = 1.68 95% CI 1.10-2.58). No association was found for the gene XRCC1 (OR = 0.82 95% CI 0.53-1.27). The combined analysis for both genes did not show association with this neoplasia (OR = 1.27 95% CI 0.79-20.5). The relationship of XRCC1 and APEX1 genotypes with cancer aggressiveness through the correlation with histopathological parameters, did not find any association. Our results suggest that the polymorphism in the gene APEX1 may be indicated as a potential marker for prostate cancer risk.