Biomarkers for Systemic Therapy in Metastatic Breast Cancer: ASCO Guideline Update

ASCO guideline update by Henry, Somerfield, Dayao, Elias and colleagues, from a systematic review of 19 studies published January 2015 to January 2022. Candidates for a PI3K inhibitor regimen should be tested for PIK3CA mutations by next-generation sequencing of tissue or plasma ctDNA; candidates for PARP inhibitors should be tested for germline BRCA1 and BRCA2 pathogenic variants (evidence insufficient for PALB2); candidates for immune checkpoint inhibitors should be tested for PD-L1 expression in tumour and immune cells for pembrolizumab with chemotherapy, and for mismatch repair deficiency or microsatellite instability and tumour mutational burden; NTRK fusion testing may be used. Data were insufficient to recommend routine testing for ESR1 mutations, homologous recombination deficiency or TROP2 expression, or routine ctDNA or circulating tumour cell monitoring of response.