In a recent publication, patient-derived xenograft (PDX) model, tumours grown in the presence of obesity-altered adipose stem cells in SCID/beige mice had increased circulating HLA1+ human cells as well as increased numbers of CD44+CD24− cancer stem cells in the peripheral blood, the authors concluded leptin produced by obesity-altered adipose stem cells promotes metastasis. Here, CD44 is linked to obesity due to melanocortin 4 receptor deficiency.