The Ki-67 index cut-off value of > 55% was chosen based on previous studies such as the NORDIC NEC study (median OS of 14 versus 10 months, p < 0.001) (Sorbye et al. 2013) and Milione et al. (p < 0.0001) (Milione et al. 2017) and resulted in a clear separation of the survival curves of our patients (median OS of 43.9 versus 12.7 months, p < 0.001). Here, MKI67 is linked to neuroendocrine carcinoma.