ATRX and neoplasm: A specific problem arises when pathologists identify an IDH‐mutant tumor, and either ATRX immunohistochemistry is unavailable, or ATRX immunohistochemistry is equivocal (as was shown in Case 4 of Figure 6A) or negative due to copy number loss involving the ATRX locus in a tumor with 1p/19q codeletion.