Familial adenomatous polyposis (FAP) is an autosomal dominant inherited disorder characterized by multiple colorectal adenomas. Desmoid tumors (DT) are a well-known extracolonic manifestation of FAP that frequently develop in the mesentery, retroperitoneum, and/or abdominal wall in patients with FAP. DT negatively impact the quality of life and affect survival. Due to their unclear natural course and insufficient data, there is no established evidencebased medical treatment for DT. In this article, we describe the diagnosis and treatment for DT in patients with FAP, and propose a classification system for the severity of FAP-related DT, with the aim of establishing a standard treatment for this condition.

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Peutz-Jeghers syndrome (PJS) is a rare disease characterized by the presence of hamartomatous polyposis throughout the gastrointestinal tract, except for the esophagus, along with characteristic mucocutaneous pigmentation. It is caused by germline pathogenic variants of the STK11 gene that exhibits an autosomal dominant mode of inheritance. PJS may be identified by multigene panel testing in patients with cancer. In this syndrome, there is persistent development of hamartomatous polyps in the small bowel. Such polyps may cause bleeding, intestinal obstruction, and intussusception as they grow larger. The initial gastrointestinal surveillance should be performed at about eight years of age even if no symptoms are present. Endoscopic polypectomy should be performed for small bowel polyps with a diameter of 10-15 mm or larger. Appropriate surveillance is required because patients with this syndrome may develop malignant tumors of different organs such as the digestive tracts, breasts, pancreas, uterus, ovaries, lungs, and testes. The present clinical guidelines explain the principles in the diagnosis and management of PJS, together with four clinical questions and corresponding recommendations. The guidelines have been designed to promote seamless implementation of accurate diagnosis and appropriate management of pediatric, adolescent and adult patients with the disease.

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Juvenile polyposis syndrome (JPS) is a rare disease characterized by multiple hamartomatous polyps within the gastrointestinal tract. It is caused by germline pathogenic variants of the SMAD4 or BMPR1A. Approximately 75% of newly diagnosed cases have an autosomal-dominantly inherited condition, whereas 25% are sporadic without previous history of polyposis in the family pedigree. CS/PHTS may be identified by multigene panel testing in patients with cancer. JPS is classified into three categories according to phenotypic features of polyp distribution. These include generalized juvenile polyposis, juvenile polyposis coli, and juvenile polyposis of the stomach. Juvenile polyposis of the stomach is caused by germline pathogenic variants of SMAD4 with a high risk for the development of gastric cancer. Pathogenic variant of SMAD4 is also associated with hereditary hemorrhagic telangiectasia-JPS complex, which needs regular survey for cardiovascular system. The present clinical guidelines explain the principles in the diagnosis and management of JPS, together with three clinical questions and corresponding recommendations. The guidelines have been designed to promote seamless implementation of accurate diagnosis and appropriate management of pediatric, adolescent and adult patients with the disease.

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Cowden syndrome (CS)/PTEN hamartoma tumor syndrome (PHTS) is an autosomal-dominantly inherited rare condition caused by germline pathogenic variants of the PTEN gene. It is associated with multiple hamartomatous lesions in various organs and tissues, including the gastrointestinal tract, skin, mucous membranes, breast, thyroid, endometrium, and brain. Macrocephaly or multiple characteristic mucocutaneous lesions commonly develop by twenties. This syndrome is occasionally diagnosed in childhood by multiple gastrointestinal lesions, autism spectrum disorders, and intellectual disability. CS/PHTS may be identified by multigene panel testing in patients with cancer. Appropriate surveillance is required because patients may develop malignant tumors such as the breast cancer, thyroid cancer, endometrial cancer, colorectal cancer, and renal cancer. The present clinical guidelines explain the principles in the diagnosis and management of CS/PHTS, together with four clinical questions and corresponding recommendations. The guidelines have been designed to promote seamless implementation of accurate diagnosis and appropriate management of pediatric, adolescent and adult patients with the disease.

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