Influence of the phenotype on mycosis fungoides prognosis, a retrospective cohort study of 160 patients.

Background: Mycosis fungoides (MF) typically has a CD4 CD8 T-cell phenotype. Rare cases of CD4 CD8 , CD4 CD8 , or CD4 CD8 immunophenotypes have been described. Little is known about the impact of MF immunophenotypes on disease behavior.

Methods: We conducted a retrospective cohort study to review all cases of MF from 2007 to 2017 from Sunnybrook Health Sciences Centre, Toronto, Canada. CD4 CD8 (Group 1) was compared to the three less common subtypes (Group 2) with respect to stage at diagnosis, progression, and transformation. Potential confounding factors (demographic, clinical, and laboratory parameters) were assessed.

Results: A total of 160 patients with confirmed MF were analyzed, including 126 CD4 CD8 MF (79%), 26 CD4 CD8 MF (16%), six CD4 CD8 MF (4%), and two CD4 CD8 MF (1%). Both groups were similar with respect to demographics and laboratory parameters at the time of diagnosis. There was no difference between patients with late stage disease (10% vs. 9%) for groups 1 and 2, respectively (P = 0.901). There was no statistically significant difference either in 5-year progression (27.7% vs. 23.5%, P = 0.283) or transformation (16.2% vs. 17.3%, P = 0.350) estimates. We did find that atypical immunophenotypes presented with different clinical morphologies and were less likely to require systemic therapy.

Conclusion: Our large cohort study indicates that atypical MF immunophenotypes do not seem to influence prognosis. Hypopigmented MF was more frequent in the CD4 CD8 group while folliculotropic MF was exclusively seen in the CD4 CD8 group. We believe that cases of CD8 MF with aggressive behavior described in the literature represent misclassified primary cutaneous aggressive epidermotropic CD8 T-cell lymphoma. The small number of patients included in the study is a limiting factor.