In 2010, the World Health Organization categorized L-cell type neuroendocrine tumors (NETs) as tumors of uncertain malignancy, while all others were classified as malignant. However, the diagnostic necessity of L-cell immunophenotyping is unclear, as are tumor stage and grade that may guide diagnosis and management. To clarify the predictive markers of rectal neuroendocrine neoplasms (NENs), 5- and 10-year overall survival (OS) was analyzed by pathological parameters including L-cell phenotype.A total of 2,385 rectal NENs were analyzed from our previous multicenter study and a subset of 170 rectal NENs was immunophenotyped.In univariate survival analysis, tumor grade (p 10, is useful in defining L-Cell type. In this study, an L-cell immunophenotype was found in 83.5% of all rectal NENs and most, but not all L-cell type tumors were NET G1, small (< 10 mm) and confined to the mucosa/submucosa.From these results, the biological behavior of rectal NENs does not appear to be determined by L-cell type alone but instead by a combination of pathological parameters.