Follicular dendritic cell tumour/sarcomas presenting in the thorax: clinical,

imaging and pathologic features, highlighting its common misdiagnosis

Intrathoracic follicular dendritic cell sarcoma

P Viola1, KM Vroobel2, A Devaraj3, S Jordan4, G Ladas4, M Dusmet4, MA

Montero1,5, A Rice1,5, AC Wotherspoon2, AG Nicholson1,5

1Department of Histopathology, Royal Brompton and Harefield NHS Foundation

Trust, London, UK

2Department of Histopathology, Royal Marsden Foundation Trust, London, UK

3Department of Imaging, Royal Brompton and Harefield NHS Foundation Trust,

London, UK

4Department of Thoracic Surgery, Royal Brompton and Harefield NHS

Foundation Trust, London, UK

5National Heart and Lung Institute, Imperial College, London, UK

Address for correspondence: Professor Andrew G Nicholson, Department of

Histopathology, Royal Brompton and Harefield NH Foundation Trust, Sydney St

London SW3 6NP, UK

DISCLOSURE: All authors declare no conflict of interest.

Word count: 2482

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ABSTRACT

Aims: Follicular dendritic cell sarcoma (FDCS) is a rare tumour reported to occur

occasionally in association with the hyaline-vascular type of Castleman’s disease

(HVCD). Most cases arise in lymph nodes though extranodal presentation is

described.

Methods and Results: Clinical, radiological and histological characteristics,

including diagnosis on pre-resection material, were assessed in seven

intrathoracic cases from five males and two females with a median age of 38

years. Clinical symptoms were related to mass location, six cases presenting

within central and/or posterior mediastinal compartments and one within the

lungs. PET/CTs demonstrated marked fluoro-deoxy-glucose (FDG) avidity and

the prominent vessels traversing the lesions. Four of six cases (67%) were

initially misdiagnosed. HVCD was present in three cases. Two cases with high

mitotic rates recurred after resection. All were positive for at least one of the

follicular dendritic cell markers (CD21, CD35 and CD23). Six of seven cases

(86%) show Cyclin D1 expression ranging from 5% to 90%.

Conclusions: FDCS is often misdiagnosed on biopsy and pathologists need to be

aware of the tumour to request the relevant immunohistochemistry, especially in

masses presenting in the central/posterior mediastinum with high vascularity and

SUV levels. Background HVCD appears more common than previously thought.

Keywords: Lung, mediastinum follicular dendritic cell tumour/sarcoma;

immunohistochemistry

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INTRODUCTION

Follicular dendritic cells (FDC) are stromal-derived dendritic cells, classified as

accessory cells of the immune system, which form a meshwork in primary and

secondary lymphoid follicles, and trap and present antigens to B-cells [1, 2].

Follicular dendritic cell tumour/sarcoma (FDCS) is a rare tumour defined in the

latest edition of WHO as a neoplastic proliferation of spindle/ovoid cells with

morphological and immunohistochemical features of follicular dendritic cells

(FDCs) [3]. First reported in 1986 by Monda et al. in a series of four cases [4],

both nodal (predominantly in the head and neck region) and extra nodal

presentation (including gastrointestinal system, tonsil, liver and spleen) have

since been described. However, the clinical presentation of FDCS in the thorax is

not well delineated, with only a limited number of reported cases and minimal

imaging data.

Its aetiology is also not known, although Epstein-Barr virus has been associated

with a specific subset of FDCS presenting in liver and spleen [5, 6] and there are

reports of FDCS being associated with the hyaline variant of Castleman’s

disease (HVCD) [7].

Herein, we review our experience of clinical, imaging and pathological

presentations of FDCS in the thorax, in particular assessing the breadth of

immunophenotype and pitfalls in pre-resection diagnosis, and its association with

HVCD.

METHODS

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The study included patients referred to Royal Brompton and Harefield Hospitals

NHS Foundation Trust between 2001 and 2015, with a final diagnosis of FDCS.

Criteria for inclusion were morphological and immunohistochemical:

fascicles/whorls of spindle to ovoid cells with features resembling follicular

dendritic cells and the expression of one or more specific follicular dendritic cell

markers: CD21, CD23 and CD35 [3]. Cases were reviewed collectively by both

pathologists with expertise in both lymphoreticular (ACW) and thoracic (AGN)

pathology. An additional broad immunohistochemical panel was performed

including epithelial, lymphoid and mesenchymal markers as listed in Table 1 and

we looked for the presence of HVCD. Staining was considered focal if the

percentage of positive tumour cells was between 10% and 40%. Clinical

information was obtained from hospital records and clinicians. Radiological

features of pre-operative imaging were reviewed by a thoracic radiologist (AD).

Location in the chest, presence of calcification, lesion vascularity, and PET

avidity were recorded. We also reviewed pre-resection material to assess

agreement between biopsy and final diagnosis. The project was approved by the

Royal Brompton and Harefield NHS Foundation Trust as a service evaluation

project.

RESULTS

Seven resected cases were identified that met current WHO criteria described

above [3]. The patients were five men and two women (male: female ratio of

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2.5:1) between 20 and 67 years old, median age of 38. Clinical data are

presented in Table 2.

Four patients presented with a mediastinal mass, one having four recurrences

within the study period. One patient presented with a purely intrapulmonary mass

and two further cases had a mainly mediastinal mass with direct extension into

the lung at presentation. Clinical presentation was mainly with cough, chest pain

and/or back pain. In one patient the tumour was an incidental finding. One patient

had a prior history of severe oral lichen planus, otherwise there was no

significant past medical history. No clinical information, other than age and

gender, was available in two cases. In all cases where the clinical history could

be reviewed, there was no significant family history.

Four of six cases (66.7%) biopsied prior to resection were misdiagnosed as other

pleomorphic malignant tumours. All of these were small biopsies in which the

relevant immunohistochemical stains were not applied. Favoured alternative

diagnoses were carcinoma, sarcoma, lymphoma and germ cell tumour. However,

resection specimens afforded better architecture leading to suspicion of FDCS

and appropriate immunohistochemistry to confirm the diagnosis. One case

underwent excision without initial biopsy.

Six patients had pre-operative imaging available for review, three with PET/CT,

two with contrast enhanced CT and one patient with MRI only. All cases with

available PET/CTs demonstrated marked fluoro-deoxy-glucose (FDG) avidity

(Figure 1). A notable feature in all three cases with contrast enhanced CT and

the one case with MRI was the presence of numerous vessels traversing the

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lesion (Figure 2). The location of the lesion on imaging was either central

mediastinum (n=2), or occupying both the central and posterior mediastinum

(n=3). None of the cases demonstrated calcification.

Macroscopically, tumours were variably circumscribed, and showed a

homogenous grey cut surface with haemorrhage present in two cases. Two

cases infiltrated the lung and one case arose at the hilum of the lung, being

centred on the lymph nodes, although focally infiltrating the airway (Figure 1).

Histologically all cases showed an atypical spindle cell proliferation with storiform

pattern within a mixed inflammatory stroma. In three mediastinal cases, HVCD

was present in the background (Figure 3). In all these cases, there was

evidence of FDC dysplasia Mitotic activity was highly variable, ranging from 1

per 10 high power fields (HPFs) to more than 20 in the two cases that recurred

(Table 3).

The immunohistochemistry findings are summarised in Table 4. All cases were

positive for at least one of CD21, CD23 and CD35. Four cases (57.1%) showed

co-expression of all three specific markers CD21, CD35, and CD23, one case

was positive for CD21 and CD35, one case for CD21 only and one case for

CD35 only. Three cases (42.9%) show positive staining for S100. All cases were

negative for both CD1a and cytokeratins. Two cases (28.6%) co-expressed

CD45 and CD4. In addition, immunohistochemistry for langerin, myeloperoxidase

(MPO), CD3, CD20, CD5, CD79a, CD10, FOXP3, PD1, EBV, and

pancytokeratins was negative in lesional cells in every case. Six of seven cases

(85.7%) show Cyclin D1 expression ranging from 5% to 90%.

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Four patients were treated with surgical resection alone; two patients received a

combination of chemotherapy, surgical resection, and radiotherapy and one

patient received neoadjuvant chemotherapy followed by surgical resection. The

median follow-up time was 35 months, although two patients had no follow-up

data available: one patient was alive with disease (AWD) after 9 years, two

patients had no evidence of disease (NED) and one died of disease (DOD). One

patient is recently post-operative, with uneventful follow-up to date.

DISCUSSION

This study highlights the difficulties in diagnoses of intrathoracic FDCS on biopsy,

primarily due to its rarity and requirement for IHC (CD21, CD23, CD35) that is not

typically part of a routine panel when addressing a mediastinal or intrapulmonary

mass. It also shows that FDCSs most commonly occur within central and/or

posterior compartments of the mediastinum, although may rarely be

intrapulmonary, and that a high mitotic rate may predict likelihood of recurrence.

Reported cases of FDCS describe a tumour that occurs at any age but mainly in

adults with a mean age of 46 years [2, 8-10]. There is no evidence of gender

predilection although a slight female preponderance has been reported for the

inflammatory pseudotumour-like variant [8, 11]. Our series is not dissimilar

although there is a male preponderance.

From a clinical point of view presentation appeared to be primarily related to the

location of the mass except for one patient (case 1) who was asymptomatic and

the mediastinal mass was an incidental finding on imaging.

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Our data also add to the literature on CT and PET findings for FDCS. Leipsic et

al. [12] investigated radiographic and CT findings of FDCS suggesting that this

entity should be included in the differential diagnosis of untreated bulky

mediastinal masses especially in presence of calcification. However, we found no

calcification in any of our cases, even those with HVCD, where the presence of

coarse calcification in soft-tissue-attenuation mass is considered a feature of

HVCD [13]. FDG-PET findings of primary pulmonary FDCS have been described

in only few cases, with the SUV max ranging from 3.2 – 11.4 [14, 15] with a

moderate to high metabolic activity compared to other cancers. All three cases in

which PET was available (case 2, 3 and 7) showed intense abnormal activity,

also with a high SUV in the surrounding lymph nodes that likely reflects the

background HVCD. This may reflect the expression of GLUT-1 receptors in

dendritic cells present in the lymph node, which is partially responsible for FDG

uptake in reactive lymph nodes [15]. The presence of a rich vascular network is

also of note as a feature that might point towards FDCS in a mass presenting in

central/posterior mediastinum.

In term of clinical background, an association between FDCS and paraneoplastic

pemphigus [16] and more recently also with myasthenia gravis [17] have been

reported. We identified no such findings in our series, but one patient (case 2)

had a prior history of severe oral lichen planus and cases of paraneoplastic

pemphigus presenting as lichen planus have been reported in HVCD [18, 19]. In

relation to Castleman’s disease itself, the hyaline variant (HVCD) is a form of

benign lymphoid hyperplasia with angiofollicular hyperplasia with prominent

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FDCs and small vascularized germinal centres [20] that may have hyperplastic or

dysplastic features and Chan et al. have demonstrated the transformation of

HVCD in FDCS through multiple sequential biopsies [7, 21]. There are

occasional case reports of FDCS arising on a background of HVCD, with a

quoted incidence of 10% to 20% [22], although our series showed a higher rate

(43%). This may reflect a now greater awareness of the association and

assessing background nodal tissue in more detail.

Histologically, our data are similar to those in the literature, with variable

pleomorphism, mitotic activity, and necrosis [6, 14, 23-25]. Of noted, a mitotic

rate of 20 per 10 high power fields was seen in one case with multiple

recurrences and one case that could not be completely resected due to spinal

involvement, as seen in other studies where a higher mitotic rate suggests more

aggressive behaviour [25, 26].

Although the lung is a common site for metastasis of FDCS [27], only 7 primary

cases have been reported (Table 5) [6, 14, 23-25, 28]. We describe one further

case who presented with symptoms reflecting airway compression, with incorrect

pre-surgical diagnosis of “suspicious for non-small cell carcinoma” based on an

epithelioid tumour, but with negative lung cancer-associated markers

(cytokeratins, P40, TTF-1). Only at resection, when the tumour was noted to be

centred on hilar nodes and the tumour cells were associated with a prominent

lymphoid background, was the relevant immunohistochemical panel applied and

the correct diagnosis made.

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This case reflects others in our series and the recent literature where a review of

146 extranodal cases showed that up to 29% of cases were initially

misdiagnosed, with similar different diagnoses (sarcoma, sarcomatoid

carcinoma, lymphoma) and the correct diagnosis easily reached with appropriate

immunohistochemistry [6]. Of note aberrant expression of different antibodies

such as EMA, TTF1, S-100, D2-40 and neuroendocrine markers has been

reported in several extranodal cases of FDCS presenting in the head and neck

and abdomen leading to additional diagnostic mistakes. Cytokeratin expression

was also reported twice [1, 2, 8, 9, 29, 30].

Regarding treatment, surgical excision with or without adjuvant radiotherapy or

chemotherapy is the treatment of choice for localized FDCS (Table 2).

Chemotherapy with cyclophosphamide, adriamycin, vincristine, and prednisone

(CHOP regimen) is the most frequent systemic therapy used giving transient,

partial response in some cases, with local recurrences reported in 30-40% of

cases and metastases in 30% of patients [9, 31], as seen in our data, with death

from disease in the one case that could not be completely resected due to spinal

involvement. Of note, in six of seven cases, we found Cyclin D1 expression

ranging from 5% to 90%, which has not been previously reported. Cyclin D1 is a

protein encoded by CCND1 gene required for progression through the G1 phase

of the cell cycle and many studies correlate alteration of this gene to several

tumours. Its overexpression is related to shorter patient survival and increased

metastasis [34-37] and it has been studied as a therapeutic target for different

neoplastic pathologies with promising results. Chen et al. recently published a

10

study on novel vaccine for mantle cell lymphoma targeting Cyclin D1 whilst

Dragnev et al. focused on its role as adjuvant in the treatment of aerodigestive

tract tumours [38, 39]. To our knowledge our results are novel regarding Cyclin

D1 expression in FDCS and its presence should be further considered as both a

supportive diagnostic marker and potential therapeutic target in FDCS.

We recognise the limitation of this paper being retrospective and a small series,

but this study reflects the rarity of FDCS in the thorax, as we had only 7 cases in

14 years, and we believe that our data will add to what is known about FDCS

presenting at this site.

In summary intra-thoracic FDCS is a rare tumour with nodal and extra-nodal

presentation in the thorax and pathologists need to have FDCS in their

differential diagnosis to ensure relevant immunohistochemistry is undertaken,

especially in masses presenting in the central/posterior mediastinum with high

vascularity and SUV levels. Also background HVCD may be commoner than

previously reported and a high mitotic rate may predict recurrence.

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Legend for Tables and Figures

Table 1. Most relevant immunohistochemical stains performed on the tumours in

our series.

N/A = Not available.

Table 2. Clinical details, treatment and outcome in patients with intrathoracic

follicular dendritic cell tumour/sarcomas

AWD = Alive with Disease; NED = No Evidence of Disease; DOD = Dead of

Disease; N/A = Not available.

Figure 1. (A - D). A. Case 2: PET/CT in 25 years old patient with follicular

dendritic cell sarcoma. Unenhanced CT component shows mediastinal mass

centred on the posterior mediastinum with substantial extension into the right

hemithorax. (inset) PET component demonstrates avid FDG uptake. B. Case 3:

Axial CT shows enhancing left hilar mass in 67 years old patient with follicular

dendritic cell sarcoma. C. Case 2: A large solid mediastinal mass with focal

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nodularity and pushing borders towards the lung. D. Case 3: Left lung containing

a solid tumour centred deep to the bifurcation of the main bronchus and focally

involving the bronchus itself. Microscopy showed that the majority of the tumour

was within hilar lymph nodes.

Figure 2. Case 4: Axial T2 weighted MR in 20 years old patient with Follicular

dendritic cell sarcoma shows large right hemithorax mass spanning the middle

and posterior mediastinum. Numerous vascular channels illustrate lesion

hypervascularity.

Figure 3. (A-F). A. The tumour comprises multiple discrete nodules (H&E 0.4X).

B. Castleman’s disease in the background (H&E 20X). C. Spindle cell

morphology with mild cytological atypia (H&E 20X). D. Epithelioid morphology

with moderate cytological atypia and atypical mitosis (H&E 20X). E. CD21

expression in the neoplastic cells (20X). F. Cyclin D1 expression in FDCS (10X).

Table 3. Histological features of intrathoracic follicular dendritic cell

tumour/sarcomas.

HPF = High power field

Table 4. Immunohistochemistry data on intrathoracic follicular dendritic cell

tumour/sarcomas

+ = positive; - = negative; F = focal staining

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Table 5. Meta-analysis of cases reported in the literature with primary pulmonary

intrathoracic follicular dendritic cell tumour/sarcomas/

RML = Right middle lobe, LLL = Left lower lobe; RRL= Right lower lobe; LUL=

Left upper lobe; NED = No Evidence of Disease; DOD = Dead of Disease; N/A =

Not available

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