ARID1A and cancer: To the researchers’ credit, they resampled discordant tumors to rule out if cancer heterogeneity was a factor, but additional sequencing was not able to find the mutant ARID1A. They also reevaluated the bioinformatic pipeline to look beyond the standard variant allele frequency and still could not identify the mutant ARID1A, which suggests the acquisition of the mutation during the process of becoming metastatic or being present at a very low frequency in the primary tumor.