MYC and TP53 Alterations but Not MAPK Pathway Mutations Are Common Oncogenic Mechanisms in Follicular Dendritic Cell Sarcomas

Morphological, immunohistochemical and molecular analysis of follicular dendritic cell sarcomas: L1CAM as a new diagnostic marker

AIMS

Follicular dendritic cell sarcoma (FDCS) is a rare neoplasm exhibiting morphological and immunophenotypical features of follicular dendritic cells. Given its rarity and broad morphological spectrum, diagnosis can be challenging. Knowledge of the molecular basis of this rare tumour is still limited. To further refine the biological and diagnostic characteristics of these neoplasms, we performed a comprehensive morphological, immunohistochemical and molecular analysis.

METHODS AND RESULTS

As well as histopathological and immunohistochemical analysis, we performed molecular analysis by next-generation panel sequencing of 15 tissue samples from 13 patients diagnosed with FDCS. In the histomorphological analysis of this FDCS series, we observed a morphological spectrum with a mixture of spindled and epithelioid cells (six of 13), but also cases with predominant epithelioid cytomorphology (seven of 13). We identified the L1 cell adhesion molecule (L1CAM) as a novel immunomarker of FDCS, as it was variably expressed in all cases. Sequencing led to the identification of 170 variants (classes 3, 4 and 5) in 112 genes. The most frequently detected (likely) pathogenic mutations affected NFKBIA (five of 13), leading to activation of nuclear factor kappa B (NFκB) signalling. Notably, deleterious NFKBIA mutations were only found in cases with predominant epithelioid morphology (five of seven). Furthermore, TP53 mutations were detected in two cases with epithelioid morphology and high proliferation rate, and one of these cases relapsed twice.

CONCLUSIONS

The morphological and genetic landscape of FDCS in this series was heterogeneous. However, in line with previous data, we identified recurrent genetic alterations affecting NFkB signalling. The expression of the adhesion molecule L1CAM might aid in the diagnosis of this uncommon neoplasia.

Epstein-barr virus (EBV)-positive inflammatory pseudotumor-like follicular dendritic cell sarcoma (IPT-like FDCS) presenting as thrombocytopenia: A case report and literature review

Background

Follicular dendritic cell sarcoma (FDCS) represents an exceedingly rare malignant neoplasm. Inflammatory pseudotumor-like follicular dendritic cell sarcoma (IPT-like FDCS) is recognized as a variant manifestation of FDCS. The clinical incidence of this particular disease is remarkably low, resulting in the absence of established standardized clinical protocols for its management and treatment.

Methods

Presented here is a case of primary Epstein-Barr virus (EBV)-positive splenic IPT-like FDCS, noteworthy for manifesting thrombocytopenia as its initial symptom. Our study analyzed the clinicopathologic characteristics of this case and 29 previously reported cases identified in the literature. Also, we conducted a comprehensive review of pertinent literature.

Results

We administered splenectomy to this patient and verified the diagnosis of EBV-positive IPT-like FDCS through immunohistochemical examination. Postoperatively, the patient underwent a one-year follow-up period, demonstrating no signs of recurrence. Analyzing a total of 30 cases revealed that this disease is more prevalent in female patients (F:M = 1.14:1), with a median age of 62 years. Fifteen patients were asymptomatic, and nine patients presented with abdominal discomfort or pain. All patients underwent surgical treatment. Among the cases, histopathological and immunohistochemical information was unavailable for five; however, in the remaining 25 cases, histopathology revealed a distinct inflammatory cell infiltration and spindle tumor cells arranged in sheets or fascicles. These tumor cells had vesicular chromatin and distinct nucleoli and they expressed conventional FDC markers. In situ hybridization analysis of Epstein-Barr virus-encoded small RNA (EBER) showed that all 30 cases were EBV-positive. Follow-up information showed that no patients relapsed and one (3.8 %) patient died.

Conclusion

The clinical diagnosis of EBV-positive IPT-like FDCS poses considerable challenges, necessitating a conclusive diagnosis through pathological immunohistochemical examination. EBER in situ hybridization holds significance for the definitive diagnosis of the disease. We advocate for splenectomy as the treatment of choice for limited splenic IPT-like FDCS.

EBV-Positive Inflammatory Follicular Dendritic Cell Sarcoma of the Spleen: Report of an Aggressive Form With Molecular Characterization

EBV-positive inflammatory follicular dendritic cell sarcoma (EBV+ inflammatory FDCS) is a rare neoplasm almost exclusively located in the spleen or liver. It is characterized by a proliferation of EBV-positive spindle-shaped cells bearing follicular dendritic cell markers, associated with an abundant lymphoplasmacytic infiltrate. EBV+ inflammatory FDCS is often asymptomatic or responsible for mild symptoms. It usually displays an indolent course and its prognosis is excellent after tumor removal, although relapsing and metastatic forms exist. Herein, we describe an aggressive form of splenic EBV+ inflammatory FDCS in a 79-year-old woman presenting with abdominal pain, deterioration of general health status, major inflammatory syndrome, and symptomatic hypercalcemia. A splenectomy was performed leading to a rapid improvement in her clinical condition and normalization of laboratory abnormalities. Unfortunately, her symptoms and laboratory abnormalities reappeared 4 months later. Computed tomography showed a mass in the splenectomy site and multiple liver and peritoneal nodules. Further analyses were performed on tumor tissue and showed positive phospho-ERK staining of tumoral cells indicating activation of MAPK pathway. Inactivating mutations were found on CDKN2A and NF1 genes. Subsequently, the patient's condition deteriorated rapidly. Since interleukin-6 levels were dramatically increased, tocilizumab was used but only had a transient effect on the patient's symptoms and inflammatory syndrome. Antitumor agent gemcitabine was initiated but her clinical condition continued to deteriorate and the patient died 2 weeks later. The management of aggressive forms of EBV+ inflammatory FDCS remains challenging. However, since these tumors seem to display genetic alterations, better characterization could lead to molecular targeted therapies.