Glossary

SNV classes

Considering the pyrimidines of the Watson-Crick base pairs, there are only six different possible substitutions: C>A, C>G, C>T, T>A, T>C, T>G.

References:

• Single Base Substitution (SBS) Signatures

Transitions (Ti) and transversions (Tv)

DNA substitution mutations are of two types. Transitions are interchanges of two-ring purines (A↔G) or of one-ring pyrimidines (C↔T): they therefore involve bases of similar shape. Transversions are interchanges of purine for pyrimidine bases, which therefore involve exchange of one-ring and two-ring structures.

Type	SNV classes
Ti	C>T, T>C
Tv	C>A, C>G, T>A, T>G

References:

• Transitions vs. Transversions

Tumor mutational burden (TMB)

Number of genetic alternations detected within an individual.

Variant allele frequency (VAF)

VAF is used to infer whether a variant comes from somatic cells or inherited from parents when a matched normal sample is not provided. A variant is potentially a germline mutation if the VAF is approximately 50% or 100%.

References:

• Variant Interpretation for Cancer (VIC): a computational tool for assessing clinical impacts of somatic variants