Supplementary Material for: Early Loss of Forkhead Transcription Factor, O Subgroup, Member 1 Protein in the Development of Pancreatic Ductal Adenocarcinoma

Objectives: Forkhead transcription factor, O subgroup, member 1 (FOXO1) is a regulatory protein that plays an essential role in cellular homeostasis. A biological function as a tumor suppressor has been proposed. Here, we examined FOXO1 expression in human pancreatic ductal adenocarcinoma (PDAC) and its precursor lesions. Methods: We immunohistochemically labeled tissue samples from 47 patients with PDAC for FOXO1 protein. In addition, we extracted data from the Cancer Genome Atlas and the Cancer Cell Line Encyclopedia and studied a potential association with well-established genetic variants. A publicly available microarray dataset of 102 PDAC samples was used to explore the influence of FOXO1 expression on patients’ clinical outcome. Results: Normal ductal epithelium universally expressed nuclear and cytoplasmic FOXO1. Reduced expression was observed in PanIN lesions and PDAC of all cases. Analysis of several datasets showed that the FOXO1 gene transcript levels do not correlate with KRAS, TP53, SMAD4, or CDKN2A mutation status, but positively correlate with patients’ outcomes. Conclusions: Loss of FOXO1 protein is identified as an early event during PDAC development and may be independent of the top 4 mutated cancer genes. Because of its strong expression in normal ductal cells, immunohistochemical detection of FOXO1 can function as a valuable test to establish the diagnosis of transformation and malignancy in pancreatic tissues.