We did not see frequent concurrent mutations in ARID1A and ARID1B in melanomas in the TCGA database (Table 1) (only three melanoma tumors had mutations in both ARID1A and ARID1B out of the 41 ARID1A mutated samples), suggesting the possibility that in many melanomas, there is a synthetic lethal relationship between the two paralogues. The gene discussed is ARID1B; the disease is melanoma.