Purcell et al. studied clinical samples of HB, and while 87% (85/98) of tumors showed aberrant β-catenin accumulation, the frequency of CTNNB1 mutations in their patient cohort was substantially lower [at most 20% (20/98) of samples], suggesting an alternative mechanism for β-catenin accumulation. Here, CTNNB1 is linked to hemoglobin measurement.