Unclassified Neuroendocrine Tumor with a Novel CHD4::AFF2 Fusion: Expanding the Family of AFF2-Rearranged Head and Neck Malignancies

DEK::AFF2-Associated Papillary Squamous Cell Carcinoma of the Sinonasal Tract: Clinicopathologic Characterization of 9 Cases

INTRODUCTION

DEK::AFF2 fusion-associated carcinoma, a recently recognized entity predominantly localized to the sinonasal tract and skull base, remains diagnostically challenging due to its poorly defined clinicopathological spectrum and epidemiological profile. Despite its deceptively bland histomorphology, this neoplasm is paradoxically linked to aggressive clinical behavior and elevated mortality rates.

PURPOSE

To delineate the clinicopathological and molecular characteristics of DEK::AFF2 fusion-associated carcinomas to elucidate their biological drivers and refine therapeutic strategies.

METHODS

A retrospective cohort study was conducted on some cases initially diagnosed as sinonasal papilloma of various types, with or without dysplasia or associated malignant transformation. DEK::AFF2 fusion was confirmed by DEK break-apart fluorescence in situ hybridization (FISH). Molecular features were assessed using immunohistochemistry (IHC) and in situ hybridization (ISH) to differential diagnosis. Clinical outcomes were analyzed for recurrence and disease-specific mortality.

RESULTS

Nine cases with DEK gene rearrangements were identified. The cohort comprised patients aged 51-76 years (median: 59 years), with a male predominance (M:F = 7:2). All cases demonstrated nuclear positivity for p40/p63 and AFF2 (30% ~90% tumor cells), while staining for p16 and Epstein-Barr encoded mRNA (EBER) was uniformly negative by IHC and ISH. Ki-67 index ranges from 5 to 40% with the median at 20%. Local recurrences occurred in 55.6% (5/9) of patients within 10-30 months following initial therapeutic intervention. The disease-specific mortality observed in 22.2% (2/9) of cases.

CONCLUSION

DEK::AFF2 fusion-associated carcinoma is characterized by a clinicopathological dichotomy: bland histological features contrast with aggressive biological behavior and poor prognosis in the nasal cavity, paranasal sinuses, and skull base.

DEK::AFF2 rearranged neoplasm with undifferentiated morphology and neuroendocrine phenotype in a pediatric patient

The advent of next-generation sequencing (NGS) has greatly enhanced the identification of morphologically and/or phenotypically unusual neoplasms. We report an undifferentiated carcinoma with a DEK::AFF2 fusion in a 13-year-old female from the head and neck region. DEK::AFF2 rearranged non-keratinizing squamous cell carcinoma (NKSCC) has been recognized as a distinct entity in the WHO classification of head and neck tumors, typically affecting adults. The case presented is unusual for both the patient's age and the undifferentiated morphology, which includes neuroendocrine immunophenotypic features, such as focal synaptophysin staining, dot-like cytokeratin expression, and only scattered cells positive for p63 and p40. Additional cases are needed to determine whether these features define a distinct subset of DEK::AFF2 rearranged neoplasms and to assess their potential correlation with a younger age of occurrence.

Identification of a novel TOP2B::AFF2 fusion gene in B-cell acute lymphoblastic leukemia

Genetic alterations play a pivotal role in leukemic clonal transformation, significantly influencing disease pathogenesis and clinical outcomes. Here, we report a novel fusion gene and investigate its pathogenic role in acute lymphoblastic leukemia (ALL). We engineer a transposon transfection system expressing the TOP2B::AFF2 transcript and introduce it into Ba/F3 cells. Functional studies, including proliferation, cell cycle, and apoptosis assays, were conducted to assess the fusion gene's impact. In vitro assays reveal that the TOP2B::AFF2 fusion significantly enhances Ba/F3 cell proliferation and G1/S phase transition while suppressing differentiation and apoptosis. This study identifies TOP2B::AFF2 as a potential oncogenic driver. However, further validation through in vivo studies are warranted to fully elucidate the fusion gene's role in leukemogenesis.

DEK::AFF2 Carcinoma of the Sinonasal Tract and Skull Base: A Comprehensive Review

DEK::AFF2 carcinoma is an emerging entity of the sinonasal tract and skull base, commonly exhibiting exophytic and endophytic papillary growth, complex anastomosing trabeculae, monotonous cytomorphology, acantholytic change, and tumor-infiltrating neutrophils. A subset displays overt infiltration and high-grade features akin to non-keratinizing squamous cell carcinoma. Glandular differentiation may also be rarely present. The tumor shows frequent local recurrence and occasional distant metastasis. An accurate diagnosis requires the recognition of these key histologic features, followed by molecular confirmation. Recently, AFF2 immunohistochemistry has been demonstrated to be a sensitive and specific ancillary marker. This comprehensive review summarizes the current understanding of DEK::AFF2 carcinoma.

Sinonasal Squamous Cell Carcinoma with DEK::AFF2 Rearrangement : An Aggressive Cancer with Bland Morphology

AIMS

DEK::AFF2 squamous cell carcinoma is a recently described cancer entity, with 29 cases reported to date. Occasionally, these carcinomas appear deceptively indistinguishable; however, specific morphological and phenotypic features suggest the presence of this rearrangement. However, the prognostic value of this diagnosis remains unclear. We aimed to report a new case series with histological, molecular, and clinical features.

METHODS

We collected data from 15 patients and investigated their phenotypes, including the expression profiles of CK7, P63/P40, PDL1, AFF2, and P16, morphological features, and associated prognostic data. We analyzed these data along with the previously published data.

RESULTS

Most of these cases exhibited indicative morphological features, such as exophytic and endophytic papillary growth, nuclear monomorphism, and abundant neutrophil-rich inflammatory infiltrates. Immunohistochemical analysis revealed the expression of AFF2 and squamous cell markers in all the patients. Overexpression of P16 was not detected, whereas CK7 and PDL1 were expressed variably. In our study cohort, a 50% progression or recurrence rate, 25% lymph node metastasis, 17% distant metastasis, and 18% disease-related death were identified, with a short follow-up time.

CONCLUSION

DEK::AFF2 squamous cell carcinoma incidence is probably underestimated. The low-grade appearance of these tumors sometimes limits their detection. The rates of recurrence and metastasis seem to be high despite an often bland morphology. We propose AFF2 immunohistochemistry as an effective tool, and a diagnostic algorithm has been established to support accurate diagnosis of these tumors.

DEK::AFF2 Fusion-Associated Squamous Cell Carcinoma: A Case Series with Literature Review on an Emerging and Challenging Entity

PURPOSE

DEK::AFF2 fusion-associated squamous cell carcinoma (DEK::AFF2 SCC), also reported in the literature as low-grade papillary sinonasal (Schneiderian) carcinoma (LGPSC), is a rare, primarily bland-appearing, but locally aggressive neoplasm. Morphologically, these tumors can closely resemble sinonasal papilloma (SP), especially on small or limited biopsy, often leading to misdiagnosis. DEK::AFF2 SCC is devoid of the underlying mutually exclusive EGFR or KRAS driver mutations of SP, suggesting it may represent a distinct unique entity.

METHODS

In this study, we conducted a retrospective search of "unusual" SP reported either as atypical, dysplastic, or suspicious for malignant transformation at our institution in the last 13 years (2010-2023), to identify potential cases of DEK::AFF2 SCC.

RESULTS

Of the 201 SP cases during this time period, 30 "unusual" SP cases were identified. On morphologic review of these 30 cases, 6 were worrisome for DEK::AFF2 SCC and were selected for AFF2 immunohistochemical stain (IHC), of which 3 cases were positive. All 3 AFF2 IHC positive cases were also positive for DEK::AFF2 fusion by fluorescence in situ hybridization (FISH), thereby, confirming IHC results.

CONCLUSIONS

This study highlights that AFF2 IHC can be an invaluable surrogate marker to FISH in identifying DEK::AFF2 SCC in challenging cases to avoid misdiagnosis. Detailed clinical and pathologic data were collected to gain a better understanding of this emerging challenging entity. A literature review was performed to enrich our knowledge of DEK::AFF2 SCC.

Translocations and Gene Fusions in Sinonasal Malignancies

PURPOSE OF REVIEW

During the past few years there has been an expansion in our understanding of gene fusions and translocations involved in cancer of the sinonasal tract. Here we review the downstream biologic effects, clinical characteristics, and pathologic features of these tumors. The molecular consequences and neo-antigens resulting from these chromosomal aberrations are considered and targets for current and future clinical trials discussed.

RECENT FINDINGS

Several new, clinically relevant, chromosomal aberrations have been discovered and evaluated to varying degrees in sinonasal tumors including DEK::AFF2, BRD4::NUT, ADCK4::NUMBL, and ETV6::NTRK3. Sinonasal malignancies demonstrate a diverse genetic landscape and varying clinical courses. Recent studies illustrate that gene fusions and translocations may play a role in carcinogenesis in certain sinonasal tumor subtypes and may be used to develop new biomarker-driven and patient-centered treatments.

DEK::AFF2 Fusion Carcinomas of Head and Neck

A novel DEK::AFF2 fusion carcinoma was recently described in 29 patients who originally presented with non-viral-associated nonkeratinizing squamous cell carcinoma. The tumors occurred at multiple sites in the head and neck including in the sinonasal tract, middle ear, and temporal bone. This tumor behaves aggressively involving adjacent vital structures, frequently recurs, and is inclined to develop lymph node and distant metastasis. This review aims to summarize the demographic, clinical, pathologic, immunophenotypic features, and pattern of molecular alterations as well as to discuss the differential diagnosis of DEK::AFF2 fusion carcinoma.