Hypopigmented Mycosis Fungoides With Childhood‐Onset and Middle‐Aged Onset: Two Case Reports Focusing on the Cutaneous Immune Microenvironment

ABSTRACT Hypopigmented mycosis fungoides (MF) is a rare clinical variant of MF that often presents in childhood or young adulthood and is typically associated with an indolent course. In contrast to classic MF, hypopigmented MF frequently shows a CD8 + T‐cell‐predominant phenotype, and cytotoxic immune responses have been implicated in melanocyte injury; however, the cutaneous immune microenvironment across different ages of onset remains incompletely characterized. We reported two cases of hypopigmented MF with distinct ages of disease onset and evaluated lesional immune profiles by immunohistochemistry, focusing on CD8, FOXP3, CXCL10, and CCL19. In both cases, the epidermotropic infiltrate was CD8‐positive T‐cell dominant, accompanied by scarce FOXP3‐positive cells and increased expression of CXCL10 together with CCL19. These shared features support the concept that a Tc1‐associated cytotoxic immune milieu, accompanied by scarce FOXP3‐positive cells, may be associated with hypopigmentation in hypopigmented MF, irrespective of the age at clinical presentation.