OBJECTIVE: We sought to characterize the clinical and genetic features of pustular psoriasis through the analysis of an extended patient cohort.
METHODS: We ascertained a data set of unprecedented size, including 863 unrelated patients (251 with GPP, 560 with PPP, 28 with ACH, and 24 with multiple diagnoses). We undertook mutation screening in 473 cases.
RESULTS: Psoriasis vulgaris concurrence was lowest in PPP (15.8% vs 54.4% in GPP and 46.2% in ACH, P
METHODS: We retrieved 4 previously reported SMCA, performed additional immunohistochemical and targeted next-generation sequencing (NGS). We also investigated the use of NKX3.1 as a marker for SMCA in the context of its prevalence and extent (using H-score) in a mixed cohort of retrospectively and prospectively tested head and neck lesions (n = 223) and non-neoplastic tissues (n = 66).
RESULTS: NKX3.1 positivity was confirmed in normal mucous acini as well as in mucous acinar class of lesions (5/6, mean H-score: 136.7), including mucinous adenocarcinomas (3/4), SG-IPMN (1/1), and microsecretory adenocarcinoma (MSA) (1/1). All SMCA were positive. Fluorescence in situ hybridization for SS18 rearrangements were negative in all successfully tested cases (0/3). NGS was successful in two cases (cases 3 and 4). Case 3 demonstrated a PTEN c.655C>T p.Q219* mutation and a SEC16A::NOTCH1 fusion while case 4 (clinically aggressive) showed a PTEN c.1026+1G>A p.K342 splice site variant, aTP53 c.524G>A p.R175H mutation and a higher tumor mutation burden (29 per Mb). PTEN immunohistochemical loss was confirmed in both cases and a subset of tumor cells showed strong (extreme) staining for P53 in Case 4.
CONCLUSION: Despite a partial myoepithelial phenotype, SMCA, along with mucinous adenocarcinomas/SG-IPMN and MSA, provisionally constitute a mucous acinar class of tumors based on morphology and NKX3.1 expression. Like salivary mucinous adenocarcinomas/SG-IPMN, SMCA also show alterations of the PTEN/PI3K/AKT pathway and may show progressive molecular alterations. We document the first extramammary tumor with a SEC16A::NOTCH1 fusion.