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- Allelic expression imbalance of PIK3CA mutations is frequent in breast cancer and prognostically significantPublication . Correia, Lizelle; Magno, Ramiro; Xavier, JM; Almeida, Bernardo; Duarte, Isabel; Esteves, Filipa; Ghezzo, Marinella; Eldridge, Matthew; Sun, Chong; Bosma, Astrid; Mittempergher, Lorenza; Marreiros, Ana; Bernards, Rene; Caldas, Carlos; Chin, Suet-Feung; Maia, Ana-TeresaPIK3CA mutations are the most common in breast cancer, particularly in the estrogen receptor-positive cohort, but the benefit of PI3K inhibitors has had limited success compared with approaches targeting other less common mutations. We found a frequent allelic expression imbalance between the missense mutant and wild-type PIK3CA alleles in breast tumors from the METABRIC (70.2%) and the TCGA (60.1%) projects. When considering the mechanisms controlling allelic expression, 27.7% and 11.8% of tumors showed imbalance due to regulatory variants in cis, in the two studies respectively. Furthermore, preferential expression of the mutant allele due to cis-regulatory variation is associated with poor prognosis in the METABRIC tumors (P = 0.031). Interestingly, ER-, PR-, and HER2+ tumors showed significant preferential expression of the mutated allele in both datasets. Our work provides compelling evidence to support the clinical utility of PIK3CA allelic expression in breast cancer in identifying patients of poorer prognosis, and those with low expression of the mutated allele, who will unlikely benefit from PI3K inhibitors. Furthermore, our work proposes a model of differential regulation of a critical cancer-promoting gene in breast cancer.
- Germline allelic expression of genes at 17q22 locus associates with risk of breast cancerPublication . Esteves, Filipa; M Xavier, Joana; Ford, Anthony M.; Rocha, Cátia; Pharoah, Paul D. P.; Caldas, Carlos; Chin, Suet-Feung; Maia, Ana-TeresaIntroduction: Translation of genome-wide association study (GWAS) findings into preventive approaches is challenged by the identification of the causal risk variants and the understanding of the biological mechanisms by which they act. We present using allelic expression (AE) ratios to perform quantitative caseecontrol analysis as a novel approach to identify risk associations, causal regulatory variants, and target genes. Methods: Using the breast cancer (BC) risk locus 17q22 to validate this approach, we measured AE ratios in normal breast tissue samples from controls and cases, as well as from unmatched blood samples. Then we used in-silico and in-vitro analysis to map and functionally characterised candidate causal variants. Results: We found a significant shift in the AE patterns of STXBP4 (rs2628315) and COX11 (rs17817901) in the normal breast tissue of cases and healthy controls. Preferential expression of the G-rs2628315 and A-rs17817901 alleles, more often observed in cases, was associated with an increased risk for BC. Analysis of blood samples from cases and controls found a similar association. Furthermore, we identified two putative cis-regulatory variants - rs17817901 and rs8066588 - that affect a miRNA and a transcription factor binding site, respectively. Conclusion: We propose causal variants and target genes for the 17q22 BC risk locus and show that using AE ratios in caseecontrol association studies is helpful in identifying risk and mapping causal variants.