Abstract: Disclosed here is a composition comprising a primer that is (a) a loopable primer comprising a target-specific section, an adaptor section, and a stem-forming section, wherein the stem-forming section is hybridizable to a portion of the target-specific section to form a stem structure, or (b) a split primer comprising a first target-specific section, a second target-specific section, and an adaptor section positioned between the first target-specific section and the second target-specific section, or (c) a split-loopable primer comprising a first target-specific section, a second target-specific section, a stem-forming section positioned between the first target-specific section and the second target-specific section, and an adaptor section, or comprising a first adaptor section, a second adaptor section, a stem-forming section positioned between the first adaptor section and the second adaptor section, and a target-specific section.

Abstract: The invention provides methods and compositions for detecting a mutation in a target gene in a sample of blood or a fraction thereof, including in certain examples, a fraction that includes circulating tumor DNA. The methods can include a tiling PCR reaction, for example a one-sided multiplex tiling reaction. Virtually any type of mutation can be detected with the methods and compositions. In certain embodiments, gene fusions are detected. Improved PCR methods, especially for performing nested multiplex PCR reactions are provided.