(a) Schematic for histological classification of cases in the TCGA and MSK clinical IMPACT cohorts, (b) Schematic for case selection in the TCGA and MSK clin ical IMPACT cohorts, (c) Frequency of case diagnoses in TCGA (n = 145), MSK Clinical IMPACT (n = 617) and our autopsy (n = 123) cohort. (d) Representative digital images of adenosquamous carcinoma (ASC) (out of 3 cases), PDAC with potential squamoid feature or squamous differentiation (PDAC with potential SF/SD) (histologic diagnosis modified based on our re-review) (out of 9 cases), and poorly differentiated ductal adenocarcinoma (out of 57 cases) in TCGA. Alveolar or trabecular pattern was confirmed in ASC or PDAC with potential SF/SD. (e) Kaplan-Meier analysis showed poor prognosis of ASC or PDAC with potential SF/SD (n = 12) compared to conventional PDAC (n = 129) in TCGA cohort (P < 0.0001, Log-rank test), (f) Kaplan-Meier analysis showed poor prognosis of ASC or PDAC with potential SF/SD (n = 70) compared to conventional PDAC (n = 494) in MSK-IMPACT cohort (P = 0.001, Log-rank test).