Given that in the TCGA SKCM cohort APC/CTNNB1 mutations are infrequent but have an adverse prognosis only in metastatic cutaneous melanoma, we sought to investigate their theragnostic significance in a much larger and more contemporary MM patient cohort with known APC/CTNNB1 mutations and measurable disease. The gene discussed is CTNNB1; the disease is Miyoshi myopathy.