Immunophenotyping on simultaneously occurring plaques and tumours in mycosis fungoides and Sézary syndrome. 
Skin biopsy specimens from 15 patients with mycosis fungoides and Sézary syndrome, with simultaneously occurring plaques and tumours, were examined to assess phenotypic deviation.  We focused on immunophenotypic differences between the two types of lesions with respect to the T-cell markers CD2, CD3, CD4, CD5 and CD8.  In six patients (40%) loss of one or more T-cell markers occurred in at least one of the lesions.  Three of the patients studied (20%) showed a difference in immunophenotype between plaques and tumours, with an additional loss of one of the T-cell markers in the tumours (respectively, CD5, CD2 and CD4).  All three of these patients showed a larger number of blast cells in the tumour compared with the plaque.  No correlation between this loss of antigenicity and the prognosis was observed.  The results of this study show that different immunophenotypes can occur simultaneously in an individual patient.  Furthermore, we were able to confirm a relationship between the number of intraepidermal CD1+ cells in plaque lesions and the prognosis.