What are purities?

From the Guidelines

Purity in the context of tumor samples is defined as the fraction of cancer cells in the sample, denoted by ρ, and is a critical factor in subclonal reconstruction and cancer research. When analyzing tumor samples, it is essential to estimate the purity of the sample to accurately identify clonal and subclonal mutations 1. The purity of a tumor sample can be estimated using various methods, including the analysis of variant allele frequencies (VAFs) and copy number variations 1.

Key Considerations

• The concept of purity is closely related to the concept of cellular prevalence of clonal mutations, which is equivalent to the purity of the sample 1.
• The fraction of non-cancer cells in the tissue sample is 1-ρ, which can affect the accuracy of subclonal reconstruction 1.
• Estimating purity is crucial in cancer research, as it can impact the identification of driver mutations and the development of targeted therapies 1.

Implications for Cancer Research

• Accurate estimation of purity is essential for subclonal reconstruction, which can provide insights into the evolutionary history of tumors 1.
• Purity estimation errors can lead to incorrect identification of subclones and their phylogenetic relationships 1.
• The use of high-quality sequencing data and advanced analytical methods can help improve the accuracy of purity estimation and subclonal reconstruction 1.

From the Research

Definition of Purity

• Purity is defined as the absence of impurities, and it is not measurable directly 2
• There are two major approaches to determining the purity of a chemical compound: the absolute approach and the chromatographic approach 2

Approaches to Purity Determination

• The absolute approach is based on thermodynamic methods and can determine the total amount of impurities without detailed knowledge of the impurities 2
• The chromatographic approach gives information about the detection and determination of impurities, but requires knowledge of their nature and chemical behavior 2

Impurities and Their Origins

• Impurities can be derived from synthesis precursors, intermediates, and side-reaction products, as well as decomposition products, unwanted isomers, and polymorphs 2
• The evaluation of impurity levels is the basis for specifications of drug substances, with a total proportion of impurities of less than 1% considered a reasonable goal 2

Purity in Moral Psychology

• The concept of purity in moral psychology is complex and lacks scientific validity, with at least nine different understandings of the term 3, 4
• Purity is not a coherent construct and cannot be a distinct basis of moral judgment, but rather a loose set of themes in moral rhetoric 3
• Purity violations can be understood as abstract harms, acts perceived by some people to indirectly cause suffering 4

Studies on Purity

• A study on the relationship between prescribing of antibiotics and other medicines in primary care found that practices with high levels of prescribing of other medicines also prescribed more antibiotics 5
• A study on the distinctness and homogeneity of the purity domain in moral psychology found that purity is not a distinct and homogeneous domain, but rather overlapping with other domains such as autonomy 6