Incidence and Mortality of Mycosis Fungoides and Sezary Syndrome: A Nationwide Registry Study in Finland

This study investigated the incidence, mortality, and causes of death in Finnish patients with mycosis fungoides (MF) or Sezary syndrome (SS). The study population consisted of 450 patients with MF and 23 with SS and their 1:1 matched controls. Data were collected from nationwide Finnish healthcare registries. The average incidence of MF was 0.38 and of SS 0.02 per 100,000 persons in 2007-2019 and was highest among older adults. Patients with SS had a low 5-year overall survival of 33.5% vs 64.5% in their controls (p = 0.0046), whereas 62.3% of patients with MF were alive 10 years after diagnosis vs 71.4% of their controls (p = 0.0011). SS diagnosis (hazard ratio [HR] 11.85 [5.08, 27.65]; p < 0.001) and higher age (HR 1.07 [1.01, 1.12]; p = 0.01) were risk factors of poorer disease-specific survival. Moreover, patients with MF had a 2.38-fold [1.07, 5.27] risk of thyroid diseases (p = 0.033) and over 1.5-fold [1.17, 2.07] risk of cardiovascular diseases (p = 0.002) compared with controls. In conclusion, in the Finnish population, patients with MF or SS had a higher incidence and mortality and more late comorbidities than controls. More awareness, earlier diagnostic tools, and more effective treat-ment for MF/SS are needed.