ANPEP and squamous cell carcinoma: Since, the histology stratified analysis for CD13 did not show any prognostic effect (p value for both analyses > 0.05) for squamous cell carcinoma patients (SCC: n = 524 patients) or for adenocarcinoma patients (ACA: n = 720 patients), part of the observed positive prognostic effect of CD13 might be related to other histological subtypes than SCC or ACA, although rare in numbers.