DEK::AFF2 fusion-associated sinonasal carcinoma: A challenging entity mimicking sinonasal papilloma

Abstract

Abstract Introduction/Objective DEK::AFF2 fusion-associated sinonasal carcinoma (DEK::AFF2 SC) also reported in the literature as low-grade papillary sinonasal carcinoma (LGPSC) is a rare, bland-appearing, but locally aggressive neoplasm. Morphologically, these tumors can closely resemble sinonasal papilloma (SP), leading to misdiagnosis. DEK::AFF2 SC is devoid of the underlying EGFR or KRAS driver mutations of SP, suggesting it represents a distinct unique entity. Herein, we present a case of DEK::AFF2 SC in a 65-year-old female who was repeatedly diagnosed as recurrent/atypical SP over ten years. Methods/Case Report We first encountered our patient in 2015 when she presented for endoscopic removal of recurrent SP, her fifth recurrence since 2011. From 2015-2021, she experienced four additional recurrences which were repeatedly diagnosed as atypical SP until 2021, when a diagnosis of LGPSC was favored. Imaging (in 2015) also revealed a concurrent mastoid sinus mass with extra-cranial extension to the sigmoid sinus with bone erosion. With each recurrence, imaging showed bone erosion and pushing growth, concerning for malignancy. The current (2023) imaging showed mass extending through mastoid process into the posterior cranial fossa. Over the years, all specimens from the nasal cavity, maxillary sinus, mastoid process, and middle ear revealed confluent, bland- appearing, papillary exophytic and inverted growth of squamous epithelium forming cords, trabeculae, and nests. Neutrophilic infiltrate was more prominent interstitially than within the surface epithelium. No brisk mitoses, pleomorphism, or frank stromal invasion was identified. The tumor cells were CK5/6 and p63 immunoreactive. Ki-67 labeling index was low (~10%). Despite receiving chemo-radiotherapy, LGSPC recurred in 2023, and DEK::AFF2 fusion was identified by fluorescence in-situ hybridization. Results (if a Case Study enter NA) NA Conclusion This case highlights the challenges in diagnosing DEK::AFF2 SC. DEK::AFF2 SC should be considered in cases of recurrent/atypical SP, especially those exhibiting destructive growth patterns. The identification and association of DEK::AFF2 fusion in sinonasal carcinomas suggests the potential for targeted therapies, emphasizing the importance of early recognition. Future research is needed to explore the utility of targeted therapy in DEK::AFF2 SC management.