PD-1 staining was observed amidst many neoplastic T cells in 6/9 (67%) and 62/103 (60%) cases of SS and MF, respectively, while only 6/42 (14%) cases of CLD and 0/20 (0%) cases of CD30+ LPD. This evidence concerns the gene TNFRSF8 and congenital secretory chloride diarrhea 1.