Inclusion Criteria:

          -  Histological diagnosis of well differentiated NET (typical and atypical lung
             carcinoids, NET G1, NET G2 of all gastroenteropancreatic sites and pancreatic NET G3
             according to WHO 2017 classification) 20 advanced / metastatic, inoperable, with no
             possibility of curative treatment

          -  Immunohistochemical expression ≥ 1 percent for estrogen and / or progesterone receptor

          -  Disease with radiological progression (at least 10 percent tumor volume growth) in the
             last 12 months before day 1 cycle 1.

          -  No possibility of established treatments due to lack of access, risk of toxicities or
             without clinical indication. Patients who meet criteria for watchful waiting (low-dose
             disease and non-functioning NET) may be included.

          -  Measurable disease

          -  ECOG performance scale 0 to 2.

          -  Adequate organic function as defined by the following criteria:

               -  serum aspartate aminotransferase (AST), serum alanine aminotransferase (ALT) ≤
                  2.5 times the upper limit of local laboratory normality (ULN-LL); (up to 5xULN
                  for participants with liver metastases)

               -  Total serum bilirubin ≤ 2.0 x ULN-LL;

               -  Absolute neutrophil count ≥ 1,500 / mm^3;

               -  Platelet count ≥ 80,000 / mm^3;

               -  Hemoglobin ≥ 9.0 g / dL;

               -  Estimated creatinine clearance by the MDRD equation ≥ 30ml / min

          -  Albumin ≥ 3.5 g / dL;

          -  INR ≤ 1.5

          -  Term of free and informed consent signed by the patient or legal representative

        Exclusion Criteria:

          -  Participants already on tamoxifen, but other prior treatment are allowed

          -  Participants with aggressive disease requiring cytotoxic therapy or locoregional
             therapies (eg hepatic embolization)

          -  A history of serious clinical or psychiatric illness that, by clinical judgment, may
             involve participation risk in this study

          -  Participants participating in other protocols with experimental drugs

          -  Participants with oral food difficulties

          -  Participants who underwent major recent surgery less than 4 weeks previously

          -  Participants receiving chemotherapy or other oncologic therapy for less than 3 weeks

          -  Participants who use oral anticoagulation

          -  Previous history of deep vein thrombosis or pulmonary embolism in the last 12 months

          -  Pregnant or lactating participants

          -  Participants with postmenopausal vaginal bleeding with no defined etiology

          -  Participants with breast cancer who need to use tamoxifen for this neoplasm

          -  Another synchronous neoplasm that requires systemic treatment