Furthermore, to investigate if total STAT3/5 protein expression and activation are prominent in L‐CTCL patient tumor tissue, we performed immunohistochemical staining of skin biopsy sections from P1 to P6, as well as from five healthy individuals (H1–H5), using CD3 as a T‐cell marker, and STAT3, STAT5A, STAT5B, and pY‐STAT5 as markers of STAT5 activation. Here, STAT5B is linked to primary cutaneous T-cell non-Hodgkin lymphoma.