# Ultrastructural and Immunohistochemical Study of a Gastric Bizarre Leiomyoma: Bizarre Nuclei and Prominent Cytoplasmic Processes Extending Into and Displacing the Stroma

## TL;DR

This paper reports a rare case of a gastric tumor with unusual cell features and provides detailed structural and chemical analysis.

## Contribution

The first detailed ultrastructural and immunohistochemical analysis of a primary gastric bizarre leiomyoma.

## Key findings

- Tumor cells have bizarre nuclei and cytoplasmic processes containing filamentous fibers.
- α-smooth muscle actin and caldesmon are immunopositive in tumor cells and stroma-like regions.
- Original stromal areas are reduced to narrow gaps between tumor cells.

## Abstract

This study presents the ultrastructural and immunohistochemical findings of a gastric bizarre leiomyoma arising in the vestibule of a 79‐year‐old male. Histologically, loosely proliferating tumor cells consist of large, multinucleated, bizarre nuclei with intranuclear inclusions and abundant cytoplasm‐containing vacuoles. A murky line was apparent between the tumor cells and eosinophilic and heterogenous stroma‐like areas. Immunohistochemically, tumor cells exhibited positively stained dot patterns of α‐smooth muscle actin and caldesmon, which were distributed in the cytoplasm of tumor cells and stroma‐like regions. Ultrastructurally, tumor cells exhibited extended and complex cytoplasmic processes comprising the fascicles of filamentous fibers. These structures were also detected in the apparent stroma‐like regions observed histologically and were consistent with the α‐smooth muscle actin‐ and caldesmon‐immunopositive dot structures. The original stromal areas remained as considerably narrow gaps between tumor cells with extended cytoplasmic processes. To the best of our knowledge, this is the first report detailing the unique ultrastructural and immunohistochemical characteristics of tumor cells and the limited stromal composition of an extremely rare primary gastric bizarre leiomyoma.

In this report, we describe an extremely rare case of primary gastric bizarre leiomyoma that is histologically consistent with leiomyoma with bizarre nuclei in the uterus. Ultrastructurally, tumor cells had extended and complex cytoplasmic processes comprising the fascicles of filamentous fibers which were also detected in the apparent stroma‐like regions observed histologically and were consistent with the caldesmon‐immunopositive dot structures. We reveal the distinctive characteristics of tumor cells and the limited stromal composition of this neoplasm.