CDK4 and acral lentiginous melanoma: ALM cell lines and patient-derived xenograft (PDX) models with CDK4 pathway alterations were reported to exhibit elevated in vivo sensitivity to CDK4/6 inhibitors (CDK4i/6i) [7], which provided rationale for the first phase II clinical trial (NCT03454919) of palbociclib in patients with advanced ALM whose tumors exhibit CDK4-pathway aberrations [8].