A Periadrenal Gland Ewing Sarcoma With Extensive Posttreatment Ganglioneuroblastoma-Like Morphology in an Adult Patient

Abstract

Neuroblastoma and Ewing sarcoma are two round cell malignancies that can exhibit light microscopic overlap and potentially arise in the same anatomic location, leading to diagnostic uncertainty. Neoadjuvant chemotherapy-induced cytodifferentiation/maturation is a common feature in pediatric malignancies, whereas Ewing sarcomas often exhibit variable degrees of necrosis, inflammatory infiltrates, and stromal fibrosis after neoadjuvant treatment. Posttreatment neuroblastoma-like morphologic changes have been rarely reported in pediatric Ewing sarcoma. Herein, we report a 33-year-old man with a retroperitoneal periadrenal mass and normal plasma catecholamine levels. The tumor biopsy demonstrated Homer-Wright rosette-forming small round cells with a high nuclear-to-cytoplasmic ratio and finely granular chromatin. The tumor cells showed strong, diffuse membranous CD99 and nuclear NKX2.2 expression, whereas they were negative for PHOX2B, a neuroblastoma/ganglion cell marker. EWSR1 rearrangement detected by FISH confirmed the light microscopic impression of Ewing sarcoma. The postchemotherapy resection showed a biphasic tumor with a predominantly ganlioneuroblastoma-like morphology and a minor component of round cell sarcoma. The round cell sarcoma area retained membranous CD99 but was negative for NKX2.2. The ganglioneuroblastoma-like areas retained NKX2.2 immunoreactivity, remained negative for PHOX2B, and were additionally negative for CD99. EWSR1 rearrangement by FISH was observed in the resection specimen. Our report shows a rare example of chemotherapy-induced cytodifferentiation resembling ganglioneuroblastoma in an adult patient with conventional Ewing sarcoma.

Introduction

Ewing sarcoma is a “small round cell” sarcoma with skeletal predilection. Nearly 80% patients are younger than 20 years of age. Extraosseous (soft tissue) tumors are more commonly encountered in older patients. ¹ Histomorphologically, most Ewing sarcomas are composed of uniform small round cells with scant, clear, or eosinophilic cytoplasm and rounded nuclei with finely granular chromatin. Some fusion-positive examples exhibit neuroectodermal differentiation, with well-formed Homer-Wright rosettes, and were previously classified as primitive neuroectodermal tumors. ¹ Regardless of morphologic variation, Ewing sarcomas are characterized by gene fusions involving one member of the FET family (most commonly EWSR1) and a member of the ETS family. ² The NKX2.2 gene is a target of the EWSR1::FL1 fusion, the most common fusion identified in Ewing sarcoma, and its protein serves as a sensitive marker for Ewing sarcoma. ³ After neoadjuvant chemotherapy, Ewing sarcomas show variable amounts of necrosis, inflammatory infiltrates, and stromal fibrosis. ⁴ Rarely, posttreatment pediatric Ewing sarcomas show neuroblastoma-like morphologic changes replete with cells resembling ganglion cells.^5–9 Neuroblastoma was historically used as an omnibus term for all types of peripheral neuroblastic tumors (pNTs). Peripheral neuroblastic tumors are neoplasia of early childhood, and the median age at diagnosis is 18 months. ¹⁰ They arise in the developing sympathetic nervous system; therefore, they occur in the adrenal medulla and/or the sympathetic ganglia. ¹⁰ Morphologically, pNTs are separated into 4 categories based on the degrees of neuroblastic/gangliocytic differentiation and the percentage of Schwannian stroma.^11,12 Differentiation of neuroblasts is manifested in the chromatin pattern, the cytoplasmic volume, and the extent of background neuropil; the latter can be seen in Homer-Wright rosettes. ¹¹ Ganglioneuroblastoma is a more differentiated subtype of pNTs, comprising more than 50% Schwannian stroma, with well-defined foci of neuroblastic cells containing more than 5% differentiating forms in abundant neuopils. ¹¹ PHOX2B, a transcription factor that acts as a key regulator of neural crest development, is a sensitive marker for neuroblastoma, regardless of neuronal differentiation or treatment status.^13,14 Neuroblasts produce catecholamines, which are metabolized into the intermediate metabolite normetanephrines, and terminal metabolites homovanilic acid and vanillylmandelic acid. ¹⁵ All of these metabolites can serve as useful ancillary laboratory tools in diagnosing neuroblastomas. ¹⁶ Herein, we report an adult patient with a large retroperitoneal Ewing sarcoma that showed Homer-Wright rosettes and conventional morphology on biopsy and extensive ganglioneuroblastoma-like change after chemotherapy. Despite morphologic similarities to a ganglioneuroblastoma, the posttreatment resection retained ESWR1 rearrangement and remained negative for PHOX2B immunoreactivity.

Patient History

The 33-year-old male patient presented with abdominal pain and fatigue, and unintentional weight loss of 30 pounds over 6 months. Both CT and MRI identified a 21-cm lobulated heterogeneous, partially necrotic left upper retroperitoneal mass that encased the left renal vein and superior mesenteric artery, crossed the midline, and displaced intra-abdominal structures (Figure 1). The mass deformed the left kidney with sinus fat infiltration, and abutted the stomach, spleen, pancreas, and the left diaphragmatic crura, eliminating fascial planes. There was no lymphadenopathy or metastatic disease on PET/CT. His plasma-free metanephrine and normetanephrine levels were within normal limits.

Figure 1.

Postcontrast CT images of the left upper quadrant abdominal mass. The suprarenal heterogeneous mass crossed the midline and displaced the intra-abdominal structures. (A) Coronal view. (B) Horizontal view.

The patient underwent an imaging-guided biopsy. Histologic examination of the needle biopsy revealed a cellular infiltrate of small, round tumor cells forming Homer-Wright rosettes (Figure 2A and B). The tumor nuclei had finely granular chromatin, occasional small but distinct nucleoli, and focal nuclear molding. Immunohistochemically, the tumor cells showed strong and diffuse membranous expression of CD99, nuclear expression of NKX2.2 (Figure 2C), and cytoplasmic expression of synaptophysin. Immunostaining for PHOX2B was negative. FISH showed a EWSR1 rearrangement (Figure 2D). The histomorphology, immunophenotype, and EWSR1 rearrangement were consistent with Ewing sarcoma/primitive neuroectodermal tumor.

Figure 2.

Biopsy of the suprarenal mass. (A) A small, round cell sarcoma with Homer-Wright rosettes (arrow) (H&E, 100× magnification). (B) Higher-power view of the Homer-Wright rosettes and nuclear molding (H&E, 400× magnification). (C) The tumor cells show nuclear immunoreactivity for NKX2.2 and strong and diffuse membranous staining for CD99 (inset) (200× magnification). (D) The tumor cells had EWSR1 break-apart signals on FISH (Orange: intact EWSR1; Red or green: break-apart) (600× magnification).

The patient underwent 14 cycles of chemotherapy with alternating vincristine, Adriamycin, cyclophosphamide, and etoposide/ifosfamide, which caused significant tumor shrinkage. Then he underwent an en bloc resection of the tumor to include distal pancreatectomy, splenectomy, nephrectomy, and adrenalectomy. Grossly, the tumor was located on the superior aspect of the kidney, abutting the diaphragm and the pancreas, with complete encasement of the adrenal gland (Figure 3). The adrenal gland appeared intact on sections. Microscopically, the posttreatment tumor showed an extensive histiocytic infiltrate and dystrophic calcifications (Figure 4). The residual viable tumor cells had a biphasic appearance (Figure 4A). The predominant component (approximately 70%) resembled ganglioneuroblastoma, with lesional cells resembling varying stages of neuronal differentiation. Dystrophic calcification was frequent in these ganglioneuroblastoma-like areas (Figure 4A). The ganglioneuroblast-like cells were embedded within abundant fibrillary neuropil-like stroma and were separated into lobules by fibrous septa (Figure 4B). More than 5% of the tumor cells in these areas had dense eosinophilic to amphophilic cytoplasm, coarsely granular to vesicular chromatin, resembling the cytodifferentiation of a neuroblast typically seen in ganglioneuroblastoma (Figure 4C). The most differentiated cells in the ganglioneuroblastoma-like component resembled ganglion cells, showing prominent nucleoli and abundant eosinophilic cytoplasm with a peripheral accentuation of the Nissl substance (Figure 4C). Within the ganlioneuroblastoma-like component, scattered tight clusters of small blue cells were present (Figure 4A and D). The tight clusters of small blue cells demonstrated strong membranous immunoreactivity for CD99 but were negative for NKX2.2 (Figure 5A and B). By contrast, the ganglioneuroblastoma-like areas were negative for membranous CD99 but retained patchy NKX2.2 expression. The round cell sarcoma areas retained minimal synaptophysin immunoreactivity, while the ganglioneuroblastoma-like areas were strongly and diffusely positive for synaptophysin (Figure 5C).

Figure 3.

Gross appearance of the suprarenal tumor. (A) The tumor encircled the intact adrenal gland (lower arrow) and abutted the spleen (upper arrow). The cut surface of the posttreatment tumor was tan-white with areas of yellow necrosis and calcification. (B) Closer view of the intact adrenal gland (arrow).

Figure 4.

Posttreatment tumor showed biphasic morphology. (A) The tumor was comprised of largely ganglioneuroblastoma-like areas (asterisk) and a small portion of conventional Ewing sarcoma (arrowhead). The arrow identifies the focus of dystrophic calcification (H&E, 40× magnification). (B) Ganglioneuroblastoma-like areas were separated into lobules by fibrous septa (arrow). Asterisk designates neuropil-like stroma (H&E, 200× magnification). (C) Ganglioneuroblast-like cells resembling varying stages of neuronal differentiation in a background of neuropil-like stroma. The inset shows a cell resembling a ganglion cell with a prominent nucleolus, ample cytoplasm, and peripheral accentuation of the Nissl substance (H&E, 200× magnification and 400× for the inset). (D) Higher-power view of the tight clusters of small cells (arrowhead) with rounded nuclei resembling the pretreatment tumor, and arrow points to foamy histiocytes (H&E, 400× magnification).

Figure 5.

CD99, NKX2.2, and synpatophysin showed preferential immunoreactivity for the posttreatment biphasic tumor. (A) The ganglioneuroblastoma-like area (asterisk) retained patchy NKX2.2 immunoreactivity, whereas the tight clusters of small blue cells (arrow) were negative for NKX2.2 (NKX2.2 immunostain, 400× magnification). (B) The tight cluster of small round sarcoma cells showed strong membranous immunoreactivity for CD99 (arrow), while the ganglioneuroblastoma-like cells (asterisk) were negative for membranous CD99 (CD99 immunostain, 400× magnification). (C) The round cell sarcoma areas (arrow) retained focal synaptophysin immunoreactivity, while the ganglioneuroblastoma-like areas (asterisk) were strongly and diffusely positive for synaptophysin (synaptophysin immunostain, 400× magnification).

Both components were negative for PHOX2B. FISH showed EWSR1 rearrangement in both components. The immunophenotype and the EWSR1 rearrangements supported the diagnosis of Ewing sarcoma with posttreatment ganglioneuroblastoma-like differentiation. This patient was well and without evidence of disease at 60-month follow-up since the initial diagnosis.

Discussion

Ewing sarcoma is a rare high-grade sarcoma typically occurring in adolescents and young adults. Skeletal Ewing sarcoma is more common than its extraskeletal counterpart, which is observed more often in older patients. ¹ Histomorphologically, Ewing sarcoma is characterized by monotonous small tumor cells with rounded nuclei exhibiting a high nuclear-to-cytoplasmic ratio and possessing scant, clear to lightly eosinophilic (glycogen-rich) cytoplasm with ill-defined borders. Ewing sarcoma with Homer-Wright rosettes was historically classified as a primitive neuroectodermal tumor. ¹ With advances in molecular diagnostics, an increasing number of Ewing-like round sarcomas are now classified as fusion-specific sarcomas, most notably the CIC-rearranged sarcoma, BCOR-associated sarcoma, and EWSR1::NFATC2 rearranged sarcoma, among others. The presence of Homer-Wright rosettes can be a rapid diagnostic clue for Ewing sarcoma in the appropriate clinical setting, before any ancillary testing is initiated. ¹⁷

Homer-Wright rosettes were first described in neuroblastomas by Dr James Homer Wright as circular masses composed of one or more rows of cells surrounding a central mass of fibrils and filamentous cell processes. ¹⁸ Peripheral neuroblastic tumor, more widely known as neuroblastoma, is generally a neoplasm of young children, arising in the adrenal medulla and/or the sympathetic ganglia. Adolescent and adult patients account for less than 5% of all pNTs. ¹⁰ In addition to a small, round cell morphology, the possible presence of Homer-Wright rosettes and synaptophysin immunoreactivity in both Ewing sarcoma and neuroblastoma, some Ewing sarcomas exhibit neuroblastoma-like morphology even without therapeutic interventions.^19,20 Distinguishing a suprarenal/retroperitoneal Ewing sarcoma from neuroblastoma in young adults is important because neuroblastomas beyond 10 years of age are chemotherapy-resistant, ¹⁰ while Ewing sarcoma generally responds to neoadjuvant chemotherapy. Rearrangement of a FET family gene (most commonly EWSR1) with an ETS family member confirms the diagnosis of small round cell sarcoma as Ewing sarcoma. ² Recurrent gene fusions have not been reported in neuroblastomas. ¹⁰ Even though the NKX2.2 gene is a target of the EWSR1::FL1 fusion, NKX2.2 is also expressed to some degree in most examples of Ewing sarcoma with EWSR1::ERG and tumors with less common EWSR1 fusions.^3,21 On the other hand, PHOX2B is a sensitive marker for neuroblastoma, marking lesional cells regardless of neuronal differentiation stage or treatment status,^13,14 and has been shown to be a reliable immunostain for differentiating neuroblastomas from Ewing sarcoma in a large number of tumors tested. ²² In our patient's initial biopsy, the tumor consisted of small round cells forming Homer-Wright rosettes, exhibited immunoreactivity for synaptophysin and NKX2.2, lacked PHOX2B expression, and showed an EWSR1 gene rearrangement. The features were diagnostic of Ewing sarcoma and militate against a neuroblastoma.

Although histomorphologically similar, Ewing sarcoma differs clinically from neuroblastoma beyond molecular diagnostics and lineage-specific immunohistochemical markers. As tumors derived from the sympathetic nervous system, neuroblastomas and their adult counterparts, pheochromocytomas/paragangliomas, produce catecholamines, with variable levels of intermediate and terminal metabolites detectable in plasma. ¹⁶ Indeed, increased plasma catecholamine levels, in conjunction with the typical small cell cytomorphology, are considered diagnostic of neuroblastoma in the absence of immunohistochemical stains. ¹⁰ Ewing sarcomas, on the other hand, have normal catecholamine excretion. ²³ Lastly, neuroblastoma tends to spread through the lymphatics with lymph node and bone marrow involvement, while Ewing sarcoma metastasizes hematogenously. Therefore, a large primary neuroblastoma around 20 cm in size often has accompanying lymphadenopathy, while a Ewing sarcoma may show pulmonary metastasis.

Chemotherapy has significantly improved survival in patients with Ewing sarcoma. ²⁴ The posttreatment changes in Ewing sarcoma include necrosis, inflammatory infiltrates, and stromal fibrosis.^1,4 In fact, the percentage of tumor necrosis was found to predict the outcome of operative treatment for nonmetastatic Ewing sarcoma. ²⁵ In our patient, the resection showed a biphasic tumor. The predominant component resembled a ganglioneuroblastoma with abundant neuropil-like substance and more than 5% tumor cells demonstrating coarsely granular, salt-and-pepper to vesicular chromatin. Different from a true ganglioneuroblastoma, the lobules of neuropil-like substances were demarcated by fibrous septa (Figure 4B) rather than Schwannian stroma. Additionally, the tumor cells were negative for PHOX2B. The posttreatment change in our patient also included dystrophic calcification, a finding commonly observed in neuroblastomas and an important clue in the radiological diagnosis of neuroblastomas in the pediatric population.^26,27 Posttreatment cytodifferentiation is a well-known phenomenon in pediatric malignancies, including rhabdomyosarcoma, Wilms tumor, medulloblastoma, and neuroblastoma.^28–30 Ewing sarcoma showing posttreatment neuroblastoma-like pathologic changes has been reported in pediatric patients (Table 1).^5–9,31 Along with our adult patient, a posttreatment biphasic tumor was observed in 5 out of 8 patients, with clusters of conventional Ewing sarcoma intermingled with neuroblastoma-like areas. The other 3 patients had only neuroblastoma-like changes posttreatment. Of note, neuroblastoma was broadly used in the literature to include the ganglioneuroblastoma subtype, which was often observed in the provided photomicrographs in the reported patients. CD99 was negative in the neuroblastoma-like areas in 6 of the 7 patients tested (including ours), whereas the EWSR1 rearrangement was retained. The latter finding would explain the retained NKX2.2 immunoreactivity in the neuroblastoma-like area in our patient. PHOX2B was consistently negative in our patient in both the initial biopsy and the posttreatment resection.

Table 1.

Summary of Reported Ewing Sarcoma With Posttreatment Neuroblastoma-Like Pathologic Changes.^a

			Biopsy				Posttherapy				Outcome
	Age	Location	Rosettes	Molecular	CD99	Synaptophysin	Morphology	Molecular	CD99 in NB-like area	Synaptophysin
Salet et al 30	8	Femur	Absent	EWSR1::FLI1	+	NA	Biphasic	EWSR1::FLI1	Negative	+	NED 21 months
Maeda et al 6	12	Radius	Absent	NA	+	Strong	NB-like 1	EWSR1::FLI1		+	DOD 30 months
Knezevich et al 5	10	Forearm 2	Present	EWSR1::FLI1	+	Focal	NB-like	absent	Minimal	+	NED 2 years
Weissferdt et al 8	11	Retroperitoneum	Absent	Rearranged	+	Focal	Biphasic	Rearranged	Negative	Negative	NED 14 months
Collini et al 7	17	Ilium	Absent	EWSR1::FLI1	+	Strong	NB-like	EWSR1::FLI1	Negative	+	NED 13 months
Arcovito et al 9	10	Scapula	Absent	NA	+	NA	Biphasic	EWSR1::FLI	Negative	+	NED 2 years
	19	Sacrum	NA	NA	NA		Biphasic	Rearranged	Negative	+	NED 5 months
Our patient	33	Retroperitoneum	Present	Rearranged	+	Strong	Biphasic	Rearranged	Negative	+	NED 60 months

Abbreviations: DOD, die of disease; NED, no evidence of disease; NA, not available.

a

1. Posttreatment resection showed neuroblastoma-like morphology, while autopsy showed round cell sarcoma in the lung and bone metastasis. 2. This was a soft tissue Ewing sarcoma of the forearm. +: positive. Biphasic: the posttherapy resection showed both round cell sarcoma and neuroblastoma-like areas.

To date, the exact molecular mechanisms responsible for cytodifferentiation in pediatric sarcomas remain unknown. With respect to prognosis, cytodifferentiation accompanied by a low mitotic index in embryonal rhabdomyosarcoma has been suggested as a rationale for discontinuing further treatment. ³² The significance of cytodifferentiation in Ewing sarcoma is unclear due to its rarity. Most reported pediatric Ewing sarcomas with posttreatment neuroblastoma-like cytodifferentiation appear to have a favorable outcome, and our adult patient was disease-free after 5 years (Table 1).

In conclusion, we report a retroperitoneal Ewing sarcoma that demonstrated Homer-Wright rosette formation on biopsy and extensive ganglioneuroblastoma-like morphology after chemotherapy. Collating the constellation of laboratory, radiology, immunohistochemical, and molecular studies assists in reaching the correct diagnosis.