Follicular dendritic cell tumour/sarcoma: a commonly misdiagnosed tumour in the thorax

Mesenchymal tumours of the pleura: review and update

Primary mesenchymal tumours of the pleura are uncommon and can be diagnostically challenging due to their overlapping histopathologic and immunophenotypic features. Herein we discuss selected mesenchymal tumours of the pleura, including solitary fibrous tumour, calcifying fibrous tumour, desmoid fibromatosis, synovial sarcoma, schwannoma, malignant peripheral nerve sheath tumour, inflammatory myofibroblastic tumour, follicular dendritic cell sarcoma, epithelioid hemangioendothelioma, and desmoplastic small round cell tumour. We review their clinicopathologic characteristics, along with an update on the relevant immunohistochemical and molecular features.

Angioimmunoblastic T-Cell Lymphoma with Exuberant CD30-Positive Follicular Dendritic Cell Proliferation in a SARS-CoV-2 Patient: The Role of Mutational Analysis to Exclude an Associated Follicular Dendritic Cell Sarcoma

Follicular dendritic cell (FDC) proliferation in angioimmunoblastic T-cell lymphoma (AITL) is still not well defined, challenging the accurate differential diagnosis between the AITL with expanded follicular dendritic cell meshwork and the combined AITL and follicular dendritic cell sarcoma (FDCS). Herein, we reported the case of a 58-year-old male with coexisting SARS-CoV-2 infection and AITL with an exuberant CD30-positive FDC proliferation, in which genetic analysis identified mutations of genes commonly involved in AITL but not in FDC sarcoma (i.e., RHOA, TET2, DNMT3A, and IDH2), thus supporting the reactive nature of the CD30-positive FDC expansion.

Thymoma: Challenges and Pitfalls in Biopsy Interpretation

The interpretation of biopsy specimens in the diagnosis of thymoma is a subject that is generally not addressed in the literature. Even though the diagnosis of thymoma may seem to be an easy step in the assessment of these tumors, in reality, it is the biopsy specimen interpretation that will be use to determine course of action in any particular patient. It may determine whether a patient is a surgical candidate or on the contrary whether a patient may be benefited the most by medical therapy. In addition, there may be conditions in which all that is required is surgical resection without any further treatment, and that the evaluation of those conditions does not necessarily required the careful pathologic staging that thymomas need. In addition, it is important to highlight that in small biopsies, there are limitations not only in terms of the cellularity and other features that may not be present in such biopsy but also the limitation in term of immunohistochemical interpretation. Herein we have attempted to highlight numerous tumoral conditions that are frequently encountered in the daily practice of mediastinal pathology, some of them pose significant problems in separating them from thymomas. Needles to say, the entire spectrum of mediastinal pathology that may at any given time mimic thymoma is well beyond the scope of this review. Furthermore, we also herein emphasize the need for proper clinical and radiologic information and correlation in order to lead to a better interpretation of the biopsy specimen. The emphasis in this review is on thymoma and their possible pitfall and shortcomings while evaluating small biopsy specimens.

Follicular dendritic cell sarcoma presenting as a thyroid mass: an unusual case report and literature review

Thyroid follicular dendritic cell sarcoma (FDCS) is an extremely rare malignancy that originates from follicular dendritic cells of the germinal centers and is characterized by the neoplastic proliferation of spindled to ovoid cells. As there have been only five cases reported in the literature until now, the diagnostic and therapeutic information available to clinicians regarding thyroid FDCS is fairly limited. To our knowledge, this is the first case report of thyroid FDCS without a history of Hashimoto’s thyroiditis. A 48-year-old woman was found to have a slow-growing mass in the left thyroid. After total thyroidectomy and left modified radical neck dissection, the specimen demonstrated morphologic and immunohistochemical features of FDCS. The patient had a favorable prognosis with no evidence of disease 11 months after tumor excision.

The role of needle core biopsies in the evaluation of thymic epithelial neoplasms

Thymic epithelial neoplasms are rare tumors derived from thymic epithelium that most often present as large anterior mediastinal masses. The vast majority of thymic epithelial neoplasms fall under the diagnostic category of thymoma, with a smaller percentage qualifying for a diagnosis of thymic carcinoma. The ability to render a definitive diagnosis on these tumors is generally hampered by their deep location and close proximity to vital structures, which makes biopsy sampling for histopathologic evaluation difficult. In recent years, the trend in medicine has been to opt for the least invasive procedure to obtain tissue samples that, by definition, implies also obtaining smaller and smaller biopsies, resulting in lesser amounts of tissue available for examination. In the mediastinum, the most common modalities for procuring biopsy samples from mass lesions include fine-needle aspiration, percutaneous core needle biopsy and video-assisted thoracoscopic biopsy. In this review, we will deal only with the role and limitations of percutaneous core biopsies in the interpretation of thymic epithelial neoplasms.

Nodal follicular dendritic cell sarcoma with four atypical histomorphologic features: an unusual case report

BACKGROUND

Follicular dendritic cell sarcoma (FDCS) is a rare malignancy. In addition to the classical histopathologic features, it has also some special morphological variants that can present a challenge in the diagnosis of this disease.

CASE PRESENTATION

A 45-year-old male who presented with a left supraclavicular mass was given a final diagnosis of FDCS after lymph node biopsy. The specimen obtained during radical resection revealed five different morphologies, including the classical histological appearance and atypical areas resembling desmoplastic infiltrative carcinoma, anaplastic large cell lymphoma (ALCL), hemangiopericytoma and classical Hodgkin's lymphoma (CHL). Immunohistochemistry was notable for positive CD21 and CD23 expression across all morphologies. Given the atypical appearance and location, the specimen was initially misdiagnosed as a metastatic carcinoma based on histology alone at an outside institution. The patient eventually underwent surgical resection followed by adjuvant chemotherapy and radiation. Despite treatment, the disease progressed, and the patient passed away 36 months after surgery.

CONCLUSIONS

This unusual case of FDCS contains four types of atypical histomorphologies within a single tumor specimen, including those resembling ALCL and hemangiopericytoma which are described here for the first time. Our report further expands the histopathologic spectrum of FDCS and may help assist in the diagnosis of other such challenging cases.

Mediastinal follicular dendritic cell sarcoma: a rare, potentially under-recognized, and often misdiagnosed disease

Background

Mediastinal follicular dendritic cell sarcoma (FDCS) is extremely rare. Due to potential under-recognization of this disease, it happens to be misdiagnosed, especially on core needle biopsy. We report 3 cases of mediastinal FDCS and provide a literature review to improve better understanding of the tumor and to reduce misdiagnosis.

Methods

Three cases of mediastinal FDCS in our clinic practice were studied, including their core needle biopsy and resected specimens, and those cases reported previously in English literature were retrieved and analyzed.

Results

The core needle biopsy of case 1 showed a tumor reminiscent of classical Hodgkin’s lymphoma (CHL), while the resected mass was finally diagnosed with FDCS combined with hyaline-vascular Castleman’s disease. Both the biopsy and resected tissue of case 2 were constitutive of the clear epithelioid cells with marked atypia. In both cases, definitive diagnoses were not made on core needle biopsy. In case 3, there were some areas morphologically similar to CHL, and some areas contained ovoid to spindle-shaped tumor cells with fascicular pattern. The analysis of 43 cases of mediastinal FDCS showed the age of patients were from 16 to 76 years old, the male to female ratio was 1.5:1, the maximal tumor diameters were 3–17 cm. 18 cases were underwent preoperative biopsy, whereas 15 (83.3%) of which were misdiagnosed initially, often as lymphoma. 32 patients had available follow-up data, the rates of recurrence, metastasis, and mortality were 12.5, 18.8 and 28.1%, respectively. Current limited data suggested no statistical differences between adverse prognosis and gender, age, tumor size, necrosis, or different therapeutics, respectively.

Conclusions

Mediastinal FDCS is a rare malignancy that has yet not been fully understood and been often misdiagnosed, particularly when making a diagnosis on core needle biopsy. Increased awareness of this enigmatic tumor is crucial to avoid diagnostic pitfalls.