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Extrapancreatic primary solid pseudopapillary tumor in the gastric antrum: Case report

Solid pseudopapillary tumors (SPTs) are low-grade tumors with low malignant potential, originating from the exocrine pancreas.1-4 Extrapancreatic locations at diagnosis are anecdotal. We describe the case of a teenager with a gastric SPT. The 14-year-old female patient consulted for malaise. Blood testing found nonhemolytic anemia (hemoglobin 44 g/L, mean corpuscular volume 64 fL), due to iron, folate, and vitamin B12 deficiencies without evident gastrointestinal bleeding. Anemia was caused by inadequate iron intake due to a poor diet and menorrhagia. She received a blood transfusion and was then supplemented with iron, folate, and vitamin B12. Two years later, she was hospitalized for epigastric pain with vomiting. Blood testing revealed inflammatory anemia (hemoglobin 95 g/L, ferritin 48 μg/L, C-reactive protein 115 mg/L). A computed tomography (CT) scan showed 20mm circumferential thickening of the pylorus (Figure 1A), which had already existed 2 years earlier (only 13 mm at that time) but was not interpreted as pathological. Upper endoscopy found prepyloric, cavitary, nonobstructive antral swelling (Figure 1B). Biopsies revealed invasion in the muscularis mucosa. The morphological appearance and the immunoprofile were in favor of a poorly differentiated infiltrating and ulcerated gastric carcinoma. Endoscopy and CT scan performed after three courses of 5-fluorouracil, oxaliplatin, and docetaxel found no reduction in the lesion, prompting a total gastrectomy. At histology, the tumor measured 5 × 4.5 × 4 cm (Figure 1C) and had a solid and pseudopapillary pattern composed of monomorphic cells surrounding small vascular cores (Figure 1D). Cytoplasm ranged from clear to eosinophilic with few periodic acid-Schiff (PAS)/PASdiastase positive intracytoplasmic hyaline inclusions. There was nuclear labeling with cyclin-D1 and focal para-nuclear dot-like CD10 positivity. There was no nuclear expression of beta-catenin (Figure 1E). Tumor cells were negative for the other markers tested: synaptophysin, TFE3, chromogranin, CD117, CD34, smooth muscle actin, desmin, S100 protein, WT1, CD99, CD45, Phox2B, TLE1, ALK, CDX2 and HER, AFP, inhibin, ER, PR, S100 protein, and cathepsin K. INI1/SMARCB1and mismatch repair protein expression were intact. Proliferative index with Ki-67 was ∼5%. Molecular analysis using next-generation sequencing identified a MET intron 13 variant of unknown significance. Heterotopic pancreatic tissue was not identified. Resection margins were free of tumor, without lymph node involvement. The final diagnosis was prepyloric extrapancreatic SPT. Two years after the diagnosis, the patient is in complete remission. Although rare, pancreatic SPTs (PSPT) are the most frequent pediatric pancreatic tumors mainly diagnosed in females1-3,5,6 at a mean age of 12.3 years.5 Children are more symptomatic1,5,7 at diagnosis than adults,3,7 presenting with abdominal pain1 or palpable mass.7 Extrapancreatic locations of SPT (EPSPT) are extremely rare, with about 30 cases in the literature (Table S1).3,8-34 Their preoperative diagnosis is extremely difficult because of nonspecific symptoms. In our patient, because of the associated folate and vitamin B12 deficiencies,we initially attributed the anemia to eating disorderwith lowmeat consumption andmenorrhagia, which are the main causes of iron deficiency in adolescents,35,36 which explained the diagnostic delay. Themain differential malignant diagnoses for an antral gastricmass are adenocarcinoma,37 gastric carcinoma,38 gastric lymphoma,39 gastrointestinal stromal tumor (GIST),40 and neuroendocrine tumors41 in adults and children. The CT scan misdiagnoses gastric tumor in 23% of these cancers.37 Endoscopy showed sensitivity of 60-61% for the detection of malignancy, whereas endoscopic sensitivity decreased to 20.8-27% for gastric lymphoma.39 Endoscopic biopsies are usually negative inGIST.40 However, these diagnoses remain extremely rare in children and adolescents.42 Benign antral masses can be antral hyperplastic polyps or lipomas43 that aremore easily recognizable. Histologic positivity for vimentin, nuclear beta-catenin, or cyclinD1, and a lack of neuroendocrine markers such as chromogranin-A usually prompt an accurate diagnosis of SPT.44 Most SPTs are positive for CD10 with a perinuclear dot pattern, and CD99 is also a reliable positive marker.44 Neuroendocrine tumors can be confused with SPT45 because they both express synaptophysin and CD56. They can also have intracytoplasmic hyaline globules such as SPTs (5% in neuroendocrine tumors45). Nuclear beta-catenin is classically positive in SPT46,47 but negative in neuroendocrine tumors.44 The absence of nuclear expression of beta-catenin, negativity for CD99, TFE3, and the absence of arguments for a neuroendocrine tumor44 led to the diagnosis of undifferentiated carcinoma initially. Only the final histological examination after gastrectomy made the diagnosis of EPSPT possible. Notably, 1.4% of SPTs are negative for vimentin,3 2.1% do not have nuclear labeling for beta-catenin,3 4.3% are CD10-negative,3 6% are negative for TFE3,44 and 18.5% are negative for synaptophysin.3 Recurrence occurs in 6.1-13.7% of children with PSPT.1,5 There are no data about recurrence in EPSPT under 18 years of age. Risk factors for relapse are age under 13.5 years at diagnosis, positive surgical margins,1 male sex, tumor rupture, venous invasion, high mitotic