Introduction/Objective Gastrointestinal stromal tumors (GIST), albeit very rare overall, with approximately 5,000 new diagnoses yearly in the US, represent the most common mesenchymal tumor involving the GI tract. particularly the stomach and small bowel. Pogress has been made in the past two decades in terms of describing pathogenesis, classification, and targeted therapy of GIST, however, their behavior is still quite challenging and unpredictable, and their prognosis remains guarded. Methods/Case Report We reviewed our institutional experience with GIST between 2010-2020; the review included surgical pathology reports, charts, and slides and we extracted data relevant for better characterization of these rare tumors. Results (if a Case Study enter NA) We identified a total of 53 GIST, with a preponderance of females (37 cases) versus males (16), and age ranging from 33yo (female) to 90yo (female). The majority of tumors were located in the stomach (39), with the remaining distributed between different locations: colon, small bowel, duodenum (3 each), esophagus and liver (2 each) and retroperitoneum (1). The GISTs ranged in size from 0.2 to 30 cm. 14 GISTs were smaller than 1 cm, with 8 of these being incidental findings: 4 associated with another tumor, 3 in sleeve gastrectomies, and 1 in a colon resected for perforated diverticulitis. Six GISTS were multiple, with 2-3 different tumors in the stomach, corresponding to a pT1m or pT2m stage. Majority of GISTs were spindled, while only 3 GISTwere mixed and 2 were epithelioid. All GIST in our review were c-kit positive. Conclusion In summary, we report data obtained from 53 resected GIST’s over a 10 year period. GIST ia a rare tumor overall, with an annual incidence of 10-20 new cases/ million, and therefore it is relatively difficult to study. Our findings confirm those reported in the literature as far as localization (preponderence of stomach), gender prevalence (female) and predominant proto-oncogen kit mutation, but shows a wider age range and interesting co-morbid associations in small, no risk GIST. These findings support the hypothesis that tumor microenvironment and host immune response are important factors in pathogenesis and provides empirical evidence that immunotherapy and immunomodulation should be studied as therapeutic additions in GIST.

Introduction/Objective Pulmonary Sclerosing Pneumocytoma (PSP)is a benign neoplasm with features of pneumocytic differentiation and dual-cell population. It is a rare tumor of adults with female predilection. The tumor is mostly asymptomatic. However, it can rarely show pleural invasion or lymph node metastasis. Presenting as a mass lesion by imaging studies frequently mandates a frozen section, which can be extremely challenging, and misdiagnosed as lung adenocarcinoma. We report a case of PSP with focal visceral pleural invasion that was submitted for frozen section. Methods/Case Report We report a case of a 57- year old female found to have a 2.5 cm nodule of the right lower lobe of lung on the CT scan. The patient underwent a wedge resection and the specimen was sent for intraoperative diagnosis. Sectioning revealed a firm, tan-white lesion measuring 2.1 x 2.0 x 1.1 cm. Frozen section diagnosis was suggestive of lepidic pattern adenocarcinoma with areas of fibrosis. Respectively, permanent section of the lesion revealed sheets of bland appearing cuboidal cells lining the papillary and sclerotic areas with round, bland appearing cells within the stroma. A few cells showed mild cytologic atypia with occasional prominent nucleoli and scattered mitotic figures were noted, besides visceral pleural invasion. Foci of atypical adenomatous hyperplasia were noted in close vicinity raising the suspicion of lepidic pattern adenocarcinoma on frozen section.The immunohistochemical staining was positive for Napsin, keratin, and CK7 in the surface cells but not in the round cells and EMA immunostain highlighted the surface cells and scattered round cells. Additional immunostains showed expression of estrogen receptor in the round cell component and TTF1 in both the round and surface components. The immunoprofile further supported the diagnosis of PSP and the elastic stain highlighted the visceral pleural involvement. Combined morphology and immunoprofile supported the diagnosis of PSP. Results (if a Case Study enter NA) NA Conclusion PSP is a rare benign neoplasm. It is important to recognize this challenging entity during intraoperative diagnosis as it can be easily mistaken for lung adenocarcinoma, especially in the presence of pleural invasion. The best treatment is still surgery for this neoplasm.