Abstract: The present invention relates to monitoring a patient's response to therapy. In order to improve the monitoring of a patient's response to therapy, a method is provided to set a plurality of allele frequency thresholds to accounting for variations among tumours and patients. As the multiple allele frequency thresholds take into account differences between genes, single-nucleotide polymorphisms (SNPs), and/or patients, the multiple allele frequency thresholds may provide significant value to improve personalized therapy selection, disease surveillance, and monitoring to improve patient outcomes.