I. Clinical manifestations and pathological histological features of SPTP Cystic solid papillary epithelial neoplasm of the pancreas is a relatively rare low-grade malignant tumor, which was first reported by Frantz in 1959. Historically the disease has been known by many names, such as solid papilloma, papillary cystic tumor, solid cystic tumor and cystic solid papillary epithelial tumor, etc. In 1996 WHO newly classified SPTP as a tumor of undetermined biological behavior or junctional malignant potential. The histogenesis of SPTP is still unclear, some believe that it originates from the small ducts of the pancreas, while others believe that it originates from the pancreatic alveoli. However, most scholars believe that SPTP originates from potential stem cells of the pancreas with the ability of multidirectional differentiation. The pathogenesis of SPTP is also unclear. Many scholars have studied the estrogen receptor, P53, and K-RAS of this tumor, but no clear correlation has been found. Some scholars believe that the pathogenesis of SPTP and pancreatic cancer are different and belong to two different genetic pathways, respectively. According to statistics, this disease accounts for 0.17%-2.5% of primary tumors of the pancreas, which is more common in young women, especially in black and East Asian young women, and rare in men, but its malignancy is higher than that of young female patients, according to statistics, 84% of patients exist under 35 years of age, and 59% of patients are under 25 years of age. Clinically, patients mostly present with an abdominal mass or abdominal pain, but 20% of patients have no clinical symptoms and are found incidentally during laparoscopic surgery or imaging, and generally all biochemical tests are normal. The tumor can occur in various parts of the pancreas, with the caudal part of the body being the most common, accounting for about 65%. Occasionally, it is reported to be located in the retroperitoneum unrelated to the pancreas and is thought to originate from ectopic pancreatic tissue. The mass is mostly ovoid, well-defined, with a fibrous envelope, mostly growing outside the pancreas, with a size of 2.5-20 cm, averaging 10 cm. hemorrhage, necrosis, cystic degeneration, and calcification may occur within the tumor. Many scholars believe that the typical pathological features of this tumor are: the general observation of the tumor is cystic solid with varying degrees of pseudocyst formation, the central part of the mass is hemorrhagic necrotic debris, surrounded by lobulated papillary light brown solid tissue. Microscopic examination showed morphologically consistent, non-isotypic tumor cells arranged in lamellar and pseudopapillary patterns, especially the pseudopapillary structure in the fibrous axis was an important marker for the diagnosis of SPTP. The characteristic ultrastructure of SPTP includes: electron microscopic observation of tumor cells containing a large number of 0.8-1.2um granular vesicles resembling zymogen with bounding membranes and uneven electron density; and circularly arranged lamellar structures in the cytoplasm. The tumor was clearly demarcated from normal pancreatic tissue, and calcification was occasionally seen in the cyst wall. Tumor growth can invade adjacent tissues, such as the stomach, duodenum, large blood vessels, etc., but tumors in the head of the pancreas rarely involve the common bile duct causing obstructive xanthogranuloma. The tumor grows slowly and the SPTP multiplication time is about 765 days. The prognosis is good, most of the tumors can be cured by complete resection, only 5% of the tumors recur locally, and very few have lymph node, liver and peritoneal metastases. Even if liver metastasis occurs, it is still better after reasonable treatment. (1) Cystic solid mass in the pancreatic area, with solid structures similar to muscle density on plain scan, mildly enhanced in the arterial phase and significantly enhanced in the portal vein phase after imaging, with hemorrhage, necrosis, and cystic areas showing hypodensity and no enhancement before and after enhancement, but their density is higher than that of water. MRI has a greater advantage than CT in showing different tissue structures inside the tumor. (2) Tumors with predominantly cystic structure or similar ratio of cystic and solid structures, with parenchymal parts showing attached nodules or “floating cloud sign”, or solid and cystic parts distributed interchangeably. (3) In tumors with predominantly solid structures, the cysts are scattered and unevenly distributed inside the lesion or under the envelope in the form of beads. (4) The tumor is round or oval in shape and may be mildly lobulated at the margins and is generally large in size, but it is less likely to cause dilatation of the common bile duct and pancreatic duct regardless of the location of the tumor in the pancreas. Even if the pancreatic duct is dilated, its degree is mild and not proportional to the size of the tumor in the pancreatic head area. (5) The tumor is generally well-defined due to envelope and pseudo-envelope formation. According to the literature, whether the envelope is intact is an important basis for judging the benign or low-grade malignancy of the tumor. (6) Calcification in the lesion is mainly circular or irregular calcification at the edge of the lesion, and in some cases, punctate calcified spots can be seen. (7) The tumor can occur in any part of the pancreas, which is non-specific and lacks diagnostic value. SPTP is a kind of low malignant pancreatic tumor with high surgical cure rate, which must be differentiated from other pancreatic tumors. (1) Teratoma: typical teratoma is not difficult to distinguish, but when accompanied by atypical calcification and lack of fat and this disease is more difficult to distinguish, age and gender have some significance in its differentiation. (2) Adenoid cell carcinoma: Mostly in elderly men, with high malignancy and poor prognosis. Imaging shows local parenchymal mass or diffuse enlargement of the pancreas, with unclear boundaries, uniform or uneven density, necrotic liquefaction in the center of the tumor, atrophy of the tail of the pancreas, disappearance of the peripancreatic fat gap, tumor invasion of blood vessels, lymph node metastasis, dilatation of the pancreatic duct and bile duct. (3) Pancreatic pseudocysts: often with a history of pancreatitis, the lesions are located inside or outside the pancreas, mostly round, with thin and uniform cyst wall and no calcification, no wall nodules. There is no interval within the capsule and no lobar changes. (4) Non-functional pancreatic endocrine cell tumors also occur in young women, manifesting as soft tissue masses in the pancreatic area, without central hemorrhage necrosis or cystic changes, liver metastases and lymph node enlargement are more common, with high density shadowing in the enhanced arterial phase.