Immunohistochemical stain of thymidine phosphorylase (TP) expression and related markers in skin-involved mycosis fungoides (MF-skin) and in a case of mycosis fungoides/Sézary syndrome cells with involved lymph nodes (LN-MF) with large cell transformation. (a) MF-skin: hematoxylin and eosin (H&E) stain. (b) MF-skin: CD4 highlights the malignant T cells in the epidermis. (c) MF-skin: TP expression is noted in malignant T cells (arrow in inset; 400x), squamous cells, and endothelial cells (arrowhead in inset; 400x). (d) An MF lymph node with large cell transformation is demonstrated: H&E stain. (e) TP stain shows positive immunoactivity in the transformed large neoplastic T cells (arrow in inset; 400x); macrophages are indicated by arrow in inset (400x). Images are from an Olympus BX41 microscope (Olympus Corp., Tokyo, Japan) processed with Qcapture Pro 5.1 (QImaging, Surrey, BC, Canada).