NENs are a heterogeneous group, including various malignancies originating from endocrinal cells. They are considered rare malignancies in the elderly (1) with a prevalence of around thirty-five / 100,000, usually seen in the GIS (around 67%) mainly at the ileum and rectum (2). They are classified according to their embryological/anatomical origin, index for proliferation (Ki-67 IHC) and functioning versus nonfunctioning (3).
NETs excrete various peptide hormones under autonomic nervous system control. Most of them express synaptophysin and chromogranin A. Rectal NETs represent around 2% of all rectal tumors mostly with benign behavior, with a prevalence of around 5.1/100,000. Tumors with a size of < 1 cm have a low metastatic risk but may rises to 60–80% if the size is increased > 2 cm as illustrated in Fig. 1 (4, 5, 11).
According to the World Health Organization W.H.O 2010 classification. The index for proliferation ki-67 and mitotic count were taken as a basis. Accordingly, Grade was specified as G1 ≤ 2%, G2 3–20%, and G3 > 20%. Mitotic count was indicated as G1 < 2, G2 2–20, and G3 > 20 at each of 10 high power fields /10HPF. TNM classification was indicated as T1a < 1 cm–, T1b 1–2 cm–, and T2 > 2 cm + according to muscularis propria invasion. 5-year survival is 87% in localized disease, and 25% in presence of distant metastasis (4, 6).