Diagnostic criteria in the early stage of MF include (a) epidermotropic lymphocytes with nuclei that are larger than the nuclei of lymphocytes in the upper dermis; (b) lymphocytes arranged along the basal membrane of the epidermis; (c) intraepidermal lymphocytes in areas with scant spongiosis (disproportionate epidermotropism) [12,16]; (d) the expression of CD2, CD3, and CD5 in less than 50% of T lymphocytes; (e) the expression of CD7 in less than 10% of T lymphocytes; and (f) the aberrant expression of CD2, CD3, CD5, or CD7 on epidermal and dermal T lymphocytes [12]. The gene discussed is CD5; the disease is mycosis fungoides.