Chemoprevention With Tamoxifen in Pre-Invasive Pancreas Mucinous Cystic Neoplasms Not Undergoing Immediate Resection

Inclusion Criteria: * Age ≥ 19 years * Clinically diagnosed pre-invasive pancreatic mucinous cystic neoplasm (MCN), measurable by cross-sectional imaging * Surgical resection of the lesion is not planned due to cyst features, patient factors or patient preference * Females of reproductive potential and males with partners of reproductive potential must agree to employ two methods contraception throughout the study and for up to 3 months following treatment. Non-child-bearing potential is defined as age 45 years or older and no menses for greater than or equal to 12 months or any age with surgical removal of the uterus and/or both ovaries. * Estimated glomerular filtration rate (eGFR) \> 30mL/min/1.73m2 * Willing and able to provide informed consent to and abide by the protocol Exclusion Criteria: * Presence of invasive pancreatic adenocarcinoma or high-grade dysplasia * Presence of a solid component or mural nodule, main pancreatic duct dilation or abrupt caliber change, obstructive jaundice, lymphadenopathy * Current or prior use of tamoxifen or another estrogen antagonist including, but not limited to, clomifene, raloxifene, fulvestrant, anastrazole; subjects who have previously used an estrogen antagonist are eligible provided the last use was at least 5 years prior to enrollment. * Current or planned use of hormonal treatments including estrogen, progesterone, androgens, hormone replacement therapy or other types of hormonal contraceptives including implants and depot …