['It has been suggested that the p300 transcriptional coactivator participates in the regulation of a wide range of cell biological processes, and mutations in p300 have been identified in various cancers.', 'To investigate p300 expression in cutaneous squamous cell carcinoma (cSCC) tissues and its effect on the outcome of patients with cSCC.', 'Immunohistochemistry (IHC) was performed on a tissue microarray to investigate p300 expression levels in cSCC tissues. Receiver operating characteristic (ROC) curve analysis, Kaplan-Meier plots and a Cox proportional hazards regression model were used to analyse the data.', 'Based on the ROC curves, we defined the cut-off score for high p300 expression as >\xa055% of tumour cells positively stained. High expression of p300 was observed in 86 of 165 (52·1%) of the cSCC samples and six of 30 (20%) of the adjacent normal skin tissue samples (P\xa0<\xa00·001). High expression of p300 was positively correlated with lymph node metastasis (P\xa0=\xa00·006) and advanced clinical stage (P\xa0<\xa00·001). In univariate survival analysis, high expression of p300 was correlated with poor patient outcomes in terms of recurrence-free survival (P\xa0=\xa00·006) and overall survival (P\xa0<\xa00·001). Moreover, p300 expression was evaluated as an independent prognostic factor in a multivariate analysis (P\xa0=\xa00·004).'] Does overexpression of p300 correlate with poor prognosis in patients with cutaneous squamous cell carcinoma?