Pustular mycosis fungoides has a poor outcome: a multicentric clinico-pathological and molecular case series study

Mycosis fungoides (MF) has usually an indolent course. However, some patients develop a more aggressive disease and few prognostic parameters have been identified. Isolated cases of pustular MF (pMF) suggest an unfavourable prognosis. We aim to describe the clinico-pathological characteristics and prognostic value of pMF. We retrospectively collected data of all cases of MF with histological pustules diagnosed from 2009 to 2020. The outcomes and clinico-pathological characteristics of pMF at diagnosis (pMFD) were compared to those of a cohort of non-pustular MF (NpMF). 33 pMF (including 22 pMFD) and 86 NpMF cases were included. The median age at diagnosis of pMF was 61 years [IQR=50-75]. The median follow-up of pMFD was 32 months [IQR=14-49]. Clinically, 33% of pMF had pustules. Large-cell transformation (LCT) occurred in 17 cases. pMFD were at a significantly more advanced-stage and more showed LCT at diagnosis than NpMF (50% vs 7%, p