Jeremiah McDole
Estrogen receptor 1 (ESR1) mutations in breast tumors were first identified nearly 30 years ago using Sanger sequencing. Since then, the technological landscape has evolved, as has our understanding of the impact these mutations have on tumor cell physiology. Given the dynamic nature of ESR1 mutation acquisition, circulating tumor DNA (ctDNA) samples appear to be the most robust source for analysis. Droplet Digital PCR (ddPCR) enables rapid, highly sensitive, cost-effective analysis of ctDNA, providing a powerful tool for this critical area of cancer research.
Approximately 70% of breast tumors express estrogen receptor α (ERα) (American Cancer Society 2017). Encoded by the estrogen receptor 1 (ESR1) gene, this receptor, via multiple molecular signaling pathways, plays a critical role in the development, progression, and metastasis of ERα+ breast cancer cells (Kurtanović et al. 2022).
Certain mutations in ESR1 impact the function of ERα and ultimately modify the physiology of tumor cells. For instance, computational modeling studies have demonstrated that many commonly detected ESR1 mutations, including Y537S, change the ligand binding domain of the receptor, locking it into a constitutively active confirmation. Further, such mutations render ERα less sensitive to antagonists, requiring significantly higher levels to inhibit molecular signaling (Pavlin et al. 2018).
These observations are supported by in vitro work involving cancer cell lines with the Y537S mutation. This cell line shows relative resistance to the well-characterized ERα antagonists drug compounds tamoxifen and fulvestrant, which are effective growth inhibitors against tumor cells with wild-type receptors (Jeselsohn et al. 2018).
While the previously mentioned studies demonstrate the importance of characterizing ESR1 mutations and understanding their role in tumor physiology, the dynamic nature of these mutations is also a highly relevant area of study. Data indicate that these mutations are either acquired under selective pressure or are present at low levels in primary tumors and clonally expanded over time (Liang et al. 2018, Martin et al. 2017, Schiavon et al. 2015). Therefore, the best source of the samples from which to reliably detect and study ESR1 mutations remains an important consideration.
Data comparing circulating tumor DNA (ctDNA) samples to matched tumor tissue demonstrate a higher rate of ESR1 mutation detection in liquid samples (Krop et al. 2016). This suggests that ctDNA samples are a more robust source of research material and likely provide better measurements of total ESR1 mutation burden than solid tissue.
Although Sanger sequencing was used to first identify ESR1 mutations in ERα+ metastatic breast tumor samples over 27 years ago, the technological landscape has evolved dramatically. Today, Droplet Digital PCR (ddPCR) provides rapid, cost effective, and ultra-sensitive detection of mutations in ctDNA samples (Zhang et al. 1997). Many researchers have taken advantage of ddPCR technology to power their ESR1 work (Chandarlapaty et al. 2016, Fribbens et al. 2016, Shaw et al. 2017, Spoerke et al. 2016). Given the importance of this area of study, Bio-Rad recently launched the ddPLEX ESR1 Mutation Detection Kit. It provides investigators with an off-the-shelf solution to analyze seven commonly studied ESR1 targets multiplexed into a single well without the bioinformatics burden of next-generation sequencing. Highly optimized to work with both formalin-fixed paraffin-embedded (FFPE) solid tissue and ctDNA samples, this kit runs on the QX600 ddPCR System, utilizing its six-color advanced multiplexing capabilities and scalable, user-friendly workflow.
Learn more about the ddPLEX ESR1 Mutation Detection Kit and the advantages it offers.
References
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