# Loss of clear cell characteristics in aggressive clear cell odontogenic carcinoma: a case report

## TL;DR

This case report describes a rare aggressive form of clear cell odontogenic carcinoma that lost its clear cell features and became more aggressive upon recurrence.

## Contribution

The first reported case of CCOC with pronounced squamous differentiation and aggressive behavior upon recurrence.

## Key findings

- The tumor cells transitioned from clear cell to epidermoid morphology after recurrence.
- The tumor exhibited aggressive features like necrosis, perineural spread, and lung metastases.
- FISH analysis confirmed the presence of the EWSR1::ATF1 gene fusion.

## Abstract

Clear cell odontogenic carcinoma (CCOC) is an odontogenic carcinoma characterized by sheets and islands of vacuolated and clear cells. The diagnosis of atypical CCOC can pose a challenge when tumor cells deviate from their characteristic clear morphology, even with the aid of genetic profiling for CCOC identification.

In this manuscript, we detailed the inaugural instance of a recurrently recurring clear cell odontogenic carcinoma (CCOC) with pronounced squamous differentiation in a 64-year-old male. The primary tumor in this individual initially displayed a biphasic clear cell phenotype. However, subsequent to the third recurrence, the clear tumor cells were entirely supplanted by epidermoid cells characterized by eosinophilic cytoplasm, vesicular chromatin, and prominent nucleoli. Notable aggressive attributes such as necrosis, conspicuous cytological malignancy, perineural dissemination, and vascular invasion were noted. Additionally, the tumor progressed to manifest lung metastases. The tumor cells exhibited positive immunoreactivity for AE1/AE3, KRT19, Pan-CK, EMA, P40, P63, CK34βE12, and P53, while they tested negative for CK35βH11, KRT7, S-100, and neuroendocrine markers. The Ki-67 proliferation index was calculated at an average of 15%. Furthermore, FISH analysis unveiled the presence of the EWSR1::ATF1 gene fusion.

This case illustrated a rare and aggressive case of CCOC characterized by significant squamous differentiation upon recurrence of the tumor.

The online version contains supplementary material available at 10.1186/s13000-024-01530-0.