To assess the utility of targeting MEK to increase the in vivo efficacy of CDK4i/6i, we implanted the WM4223 patient-derived xenograft (PDX) model, derived from a biopsy of a metastatic ALM that originated in the left foot of a 73 year old male patient, into NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice (Fig. 4A). Here, MAP2K7 is linked to acral lentiginous melanoma.