Gastroblastoma: Cytologic Findings with Resection and Molecular Correlation

Abstract

Abstract Casestudy Gastroblastoma is a rare tumor with biphasic components showing epithelial and mesenchymal differentiation. To date, <15 cases have been reported, with molecular confirmation of the recently identified MALAT1-GLI1 translocations only in a subset. Aspiration cytologic and small biopsy findings have not yet been reported. We present a case of gastroblastoma, arising in a 22-year-old female. Results A CT scan was performed, showing a 7 cm heterogeneous mass in the distal stomach and pancreas, clinically suspected to represent at gastrointestinal stromal tumor (GIST). She underwent two preoperative samples, including endoscopic ultrasound guided-fine needle aspiration and core biopsy, followed by a distal gastrectomy. Diff- Quik stained touch preparations performed on the core needle biopsy during rapid on-site evaluation showed a hypercellular neoplasm composed of large, three-dimensional aggregates of neoplastic cells in a background of numerous isolated single cells and bare nuclei. The neoplastic cells were bland with spindled to epithelioid nuclei, occasional nuclear grooves, and small nucleoli. Immunostains were only helpful in excluding GIST (CD117 and DOG1 negative). Distal gastrectomy showed a nodular/plexiform tumor with variably epithelioid to spindle cell cytology and solid to focally myxoid/microcystic architecture. Pancytokeratins CAM5.2 (patchy) and AE1/AE3 (very focal) were positive, with negative S100, SMA, Desmin, Melan-A, Inhibin, Calretinin, and Synaptophysin. Based on the age, location, histology and immunophenotype, gastroblastoma was suspected, and multiplex NGS-based fusion sequencing identified a MALAT1-GLI1 fusion. Staging studies were negative for metastasis at presentation. Conclusion Based on this experience, we recommend consideration of gastroblastoma for a gastric tumor in a young patient, especially if encountering a cytologic sample showing non-pleomorphic epithelioid and spindle cell cytology. Lack of expression of GIST, smooth muscle, neuroendocrine, and neural sheath-associated markers should particularly raise consideration of this rare neoplasm. While in this case molecular studies clinched the diagnosis upon resection, increasingly used GLI1 immunostain may be of use prospectively for diagnosis of limited samples.