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We report a case of a fibrous odontogenic lesion occurring in the maxilla of a man in his 60s. The patient presented with an asymptomatic radiolucent area related to the upper left premolar on radiography. Histological examination of the lesion obtained through an incisional biopsy revealed dense fibrous connective tissue containing small, rounded islands of odontogenic epithelium. The differential diagnoses included central odontogenic fibroma and sclerosing odontogenic carcinoma. Despite being completely different entities, the histological similarities between the two tumors raise diagnostic challenges, with fibrous connective tissue and odontogenic epithelium being the common features. Owing to the finding of unclear small or thin epithelial nests with a high nuclear-cytoplasmic ratio and despite its small size, the lesion was suspected of being malignant, and a maxillary resection was performed. Sections from the resected specimen displayed a small or tiny odontogenic epithelium with cellular atypia and invasion by epithelial cells in and around the nerve fasciculi; therefore, a final diagnosis of sclerosing odontogenic carcinoma was made. Nonetheless, the presence of an odontogenic epithelium in or around the nerve fascicles is not always an evidence of malignancy in the jaw. Caution should be exercised when differentiating invasive epithelia from epithelial residues to provide appropriate treatment.

Sclerosing odontogenic carcinoma is a rare, locally destructive neoplasm that is difficult to diagnose. In a 65-year-old man with pain and swelling in the mandible, radiographs of the mandibular anterior region revealed cortical destruction and infiltration of the soft tissue by a mass lesion. Biopsy did not yield a definitive diagnosis. In accordance with a differential diagnosis of epithelial malignant tumor of the mandible, resection of the mass, bilateral superior neck dissection, and reconstruction with abdominal muscle grafts were performed. Histopathological study revealed asymmetric nuclei and cells with endoplasmic reticulum in which islands and cords of epithelial cells with low-grade cytological features were surrounded by a dense sclerotic stroma. Immunostaining yielded positive results for cytokeratin (CK) 5/6, CK19, and p63 and negative results for CK20. Because of the rarity of the disease process, clinicians, radiologists, and pathologists collaborated closely to establish a diagnosis of sclerosing odontogenic carcinoma.

Alveolar soft part sarcoma (ASPS) is a rare soft tissue sarcoma characterized by an alveolar or organoid arrangement of polygonal tumour cells separated by fibrovascular septa. A specific fusion gene [ASPS critical region 1 (ASPSCR1)—TFE3] was detected in ASPS. Despite being a slow-growing tumour without pain and dysfunction, ASPS is characterized by early metastasis, which leads to poor prognosis. Herein, we report a rare case of primary ASPS of the cheek harbouring ASPSCR1 (exon 7)—TFE3 (exon 5) fusion gene in a 21 year-old woman. This tumour was a well-circumscribed, smooth, round mass that was clinically suspected as a benign tumour. However, histologically, it was observed that the polygonal tumour cells were arranged in solid and alveolar growth patterns. Post-operative examination of the whole body excluded the possibility of metastasis at other sites. Thus, careful immunohistochemical and genetic analyses, as well as whole-body examination, demonstrated that the tumour was a primary ASPS of the cheek.

Canalicular adenomas are uncommon benign salivary gland tumors that typically arise from minor salivary glands. They are usually solitary tumors; only a few cases of multiple tumors have been reported. We describe an unusual case of canalicular adenomas that appeared simultaneously in the buccal mucosa and upper lip of an elderly Japanese woman. Microscopic examination revealed that the tumors were composed of columnar cells in a canal-like structure and accompanied by cystic cavities. Immunohistochemical evaluation further revealed that the tumor cells were positive for CK7, CK14, and S100, whereas staining yielded negative results for β-catenin, calponin, Ki-67 protein, p63, and α-smooth muscle actin (α-SMA). We also review previous reports of cases of multiple canalicular adenomas and discuss their clinical features.

Clear cell carcinoma (CCC) is a rare epithelial malignant tumor of the salivary glands. It is characterized by tumor cells with clear cytoplasm, hyalinized stroma, and most importantly the fusion genes EWSR1-ATF1, EWSR1-CREM, and EWSR1-PLAG1. Break-apart FISH has been performed for multiple CCC cases, but direct sequencing analysis has been performed in relatively few. Herein, we report an interesting case of CCC harboring three EWSR1-ATF1 translocations: EWSR1 exon 8-ATF1 exon 4, EWSR1 exon 7-ATF1 exon 4, and EWSR1 exon 7-ATF1 exon 5. This case indicates the possibility of independent EWSR1-ATF1 gene translocations, and could provide insight into CCC tumorgenesis.

Clear cell carcinoma (CCC) is a rare low-grade malignant salivary gland carcinoma. EWSR1-ATF1 fusion has been characterized as a consistent finding in CCC, with breakpoints described between EWSR1 exon 11 and ATF1 exon 3. So far, over 100 cases of CCC harboring EWSR1 rearrangement arising from salivary gland of the oral cavity have been reported. Although EWSR1 involvement in these cases was confirmed by EWSR1 break-apart FISH indicating the translocation, sequence analysis for EWSR1-ATF1 fusion type has been reported only in three cases of CCC so far. Herein, we report a CCC case with novel EWSR1-ATF1 fusion (EWSR1 exon 15 and ATF1 exon 5) arising in minor salivary gland and review the role of the chimeric variants in some malignancies with EWSR1-ATF1 rearrangement. Current tumor was composed of the small nests of clear tumor cells and hyalized fibrous stroma. Immunohistochemically, the tumor was positive for AE1/AE3, CK5/6 and p63, negative for S100, Melan-A, SMA and CD10. After 8 months of follow-up, there are no evidence of recurrence.