Desmoplastic small round cell tumor

Ewing sarcoma/primitive neuroectodermal tumor is classically a tumor of the soft tissue or bone in children and young adults, but several cases have been described in patients of all ages. Within the last decade, the clinicopathologic spectrum of Ewing sarcoma/primitive neuroectodermal tumor has been markedly expanded by recognition that the tumor may also have a visceral origin. We describe a case of primitive neuroectodermal tumor arising in the stomach of a 66-year-old woman. The neoplasm was excised using a radical surgical procedure. Microscopically, the tumor was made up of solid nests and sheets of round cells. Immunohistochemically, the tumor cells showed immunoreactivity for CD99, S100, neuron-specific enolase, and vimentin. A multiplex real-time polymerase chain reaction assay detected an EWS-ERG fusion. To our knowledge, this is the first description of a primitive neuroectodermal tumor arising in the stomach.

(Arch Pathol Lab Med. 2005;129:107-110)

Tumors of the Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET) family are round cell sarcomas occurring mainly in young patients, the majority of whom are younger than 30 years, with a peak incidence during the second decade of life. There tends to be a broader age range for PNET, with a significant number of patients older than 40 years.1-4 These tumors show a predilection for deep soft tissues and have been described infrequently in visceral sites.1-11 We report a case of PNET occurring in the stomach of a 66-year-old woman; the diagnosis was confirmed by molecular techniques.

REPORT OF A CASE

A 66-year-old woman with no previous history of malignancy presented with melena. Endoscopie examination showed an antropyloric ulceration. A biopsy of the lesion showed a proliferation of small rounds cells with some degree of artifactual shrinkage, giving the classic appearance of a small cell carcinoma seen in small bronchial biopsies, that is, nuclear molding, elongation of the nuclei, and deformation, clumping, and diffusion of the chromatin. The immunophenotype was consistent with PNET.

Axial enhanced computed tomographic scan (level of antrum) revealed a thickened wall of the stomach with stranding of the perigastric fat and mesocolonic inflammatory changes (Figure 1). Endoscopie sonogram showed a 5-cm mass of the gastric antrum and the prepyloric area. This lesion appeared ulcerated, heterogeneous, and hypoechogenic, without calcification or transonic areas.

A gastrectomy with lymph node adenectomy was performed. The diagnosis of PNET was confirmed with the detection of the EWS/ERG fusion by a multiplex real-time polymerase chain reaction (PCR). The patient received adjuvant chemotherapy. She remained alive for 10 months after surgery before dying of the disease.

MATERIALS AND METHODS

The surgical specimens were processed and fixed in 10% neutral buffered formalin and embedded in paraffin. Four-micrometer-thick sections were stained with hematoxylin-eosin-saffron and periodic acid-Schiff. Fresh tissue appositions were stained with periodic acid-Schiff, with and without diastase. A fragment of tumor tissue was frozen and stored at -80°C.

Formalin-fixed, paraffin-embedded tissue sections were incubated with antibodies against MIC2/CD99 (1:150; Dako, Glostrup, Denmark), S100 protein (1:600; Dako), neuron-specific enolase (1:800; Dako), chromogranin A (1:300; Dako), synaptophysin (1:10; Dako), vimentin (1:450; Dako), cytokeratin AE1/AE3 (1:50; Dako), epithelial membrane antigen (1:150; Dako), leukocyte common antigen (1:150, Dako), CD34 (1:25; Dako), CD117(1:50; Novocastra, Newcastle upon Tyne, United Kingdom), antimelanoma (HMB-45) (1:100; Dako), and desmin (1:50; Dako) by a streptavidin-biotin-peroxidase complex method (ChemMate Detection Kit, Dako).

RNA was isolated using the Trizole extraction kit (Gibco BRL, Gaithersburg, Md). A total of 1 µg RNA was reverse-transcribed through random hexamers in a final volume of 20 µL using the GeneAmp RNA PCR Kit (PE Applied Biosystems, Foster City, Calif).

Real-time PCR experiments were performed in a final volume of 50 µL containing 2 µL of complementary DNA, with 200 µM each of deoxyadenosine triphosphate, deoxycytidine triphosphate, and deoxyguanine triphosphate; 400 µM of deoxyuridine triphosphate; 200 nM of each primer; 100 nM of the Taqman probe; 1.5 U AmpliTaq Gold (PE Applied Biosystems); and 0.5 U AmpErase UNG (Uracile N Glycosylase, PE Applied Biosystems). After initial steps of UNG reaction for 2 minutes at 50°C and TaqGold activation for 15 minutes at 95°C, 50 cycles of PCR were performed according to standardized procedures (denaturation at 95°C for 15 seconds, annealing at 66°C for 1 minute, and elongation at 72°C for 1.5 minutes). The primers and probes, originally described by Peter et al,12 can be obtained on request. The magnesium chloride concentration was between 3mM and 6mM. The real-time PCR was carried out using the ABI/PRISM 7700 (PE Applied Biosystems). The fluorescence data were collected during the annealing and extension phases of each cycle.

RESULTS

Macroscopic Examination

The tumor, measuring 8 × 5 cm, was tan-gray, generally firm, and occupied the submucosal layer with upward extensions to a focally ulcerated mucosal layer and downward extensions to the muscularis propria and the adipose tissue of the gastrocolic ligament.

Standard Histologie Examination

The gastrectomy specimen showed a proliferation consisting of sheets or lobules of small round cells containing darkly staining, round or oval nuclei; variable small nucleoli; frequent mitoses; and pale or eosinophilic scanty cytoplasm, except in areas where the cells were more mature and the elongated hairlike cytoplasmic extensions coalesced to form pseudorosettes (Figures 2 through 4). There was generally little stroma, but prominent fibrovascular septa could be noted, and the rich vascularity was discernible only in areas of necrosis. Vascular invasion was present. Tumor did not involve lymph nodes.

Cytologid Examination

Small blue cells were seen in groups and singly, with high nuclear-cytoplasmic ratios and nuclear molding, and some had cytoplasmic vacuoles containing PAS-positive glycogen (Figure 5).

Immunohistochemical Staining

The tumors cells were strongly and diffusely immunoreactive for CD99 and vimentin, and were focally and more weakly immunoreactive for SlOO and neuron-specific enolase (Figure 6). All other immunostains were negative.

Real-Time PCR

Molecular analysis showed the presence of the EWS-EKG fusion transcript indicative of a t(21;22)(q22;q!2).

COMMENT

Ewing sarcoma and PNET are now generally considered a single entity, the ES/PNET family of tumors.1,2,5 Virtually all ES/PNETs appear to express a chromosomal translocation resulting in fusion of the EWS gene at 22q12 with a member of the ETS-related oncogenes, that is, FL/2 (Ilq24), EKG (21q22), ETVl (7p22), EMF (17ql2), and FEV (2q33)."·14 The term primitive neuroectodermal tumor has been used for tumors that demonstrate neuroectodermal features assessed by 1 or more of the following modalities: light microscopy, immunohistochemistry, and electron microscopy.3

The most important differential diagnosis in this case (adult older than 40 years) was considered to be carcinoma (undifferentiated carcinoma or poorly differentiated neuroendocrine carcinoma). The other main differential diagnoses were considered to be lymphoma, melanoma, synovial sarcoma, rhabdomyosarcoma, and small round cell desmoplastic tumor. This differential diagnosis is further complicated by the rare or exceptional occurrence of most of these entities in the stomach.

Histochemical stains demonstrated the presence of glycogen within the tumor cells. This finding, which is nonspecific, does lend support to the diagnosis of ES and PNET.

The evidence of morphologic neural differentiation (demonstrated histologically by pseudorosettes) and of a neuroectodermal phenotype (expressed by the positivity of neuron-specific enolase and SlOO) further support the diagnosis of PNET, as does the immunoreactivity for CD99. This antibody, regularly used for diagnosing PNET, is nonspecific and positive in many tumors, particularly small round cell tumors, such as neuroendocrine carcinoma, lymphoblastic lymphoma, synovial sarcoma, alveolar rhabdomyosarcoma, solitary fibrous tumor, mesenchymal chondrosarcoma, thymoma, and small cell osteosarcoma.1,15

The diagnosis of PNET was confirmed with the detection of the EWS/ERG fusion by a multiplex real-time PCR assay, which enables the detection of the most frequent fusions observed in small round cell tumors (under identical PCR conditions), including those of Ewing tumors, alveolar rhabdomyosarcoma, synovial sarcoma, and small round cell desmoplastic tumors. This highly specific method considerably simplifies and reduces the bench work, because all the post-PCR steps are suppressed (no PCR products are manipulated, which considerably reduces the risk of cross-contamination).12

In summary, we report a case of PNET arising in the stomach (the first reported case to our knowledge). This case highlights the fact that molecular analysis is a rapid and useful tool for the diagnosis and management of these tumors, particularly when presenting in older patients and unusual sites.

We thank J. M. Coindre, MD, and O. Delattre, MD, PhD, for the reverse transcriptase-polymerase chain reaction data and for confirmation of the diagnosis. We also thank J. Franco for his technical support.

References

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6. Kawauchi S, Fukuda T, Miyamoto S, et al. Peripheral primitive neuroectodermal tumor of the ovary confirmed by CD99 immunostaining, karyotypic analysis, and RT-PCR for EWS/FLI-1 chimeric mRNA. Am J Surg Pathol. 1998;22: 1417-1422.

7. Maesawa C, lijima S, Sato N, et al. Esophageal extraskeletal Ewing's sarcoma. Hum Pathol. 2002;33:130-132.

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10. Jimenez RE, Folpe AL, Lapham RL, et al. Primary Ewing's sarcoma/primitive neuroectodermal tumor of the kidney: a clinicopathologic and immunohistochemkal analysis of 11 cases. Am J Surg Pathol. 2002:26:320-327.

11. Kushner BH, Hajdu Sl, Culati SC, Erlandson RA, Exelby PR, lieberman PH. Extracranial primitive neuroectodermal tumors: the Memorial Sloan-Kettering Cancer Center experience. Oncer. 1991:67:1825-1829.

12. Peter M, Gilbert E, Delattre O. A multiplex real-time PCR assay for the detection of gene fusions observed in solid tumors. Lab Invest. 2001 ;81:905-912.

13. Delattre O, Zucman ), Plougastel B, et al. Gène fusion with ETS DNAbinding domain caused by chromosome translocation in human tumors. Nature. 1992:359:162-165.

14. Delattre O, Zucman J, Melot T, et al. The Ewing family of tumors: a subgroup of small-round-cell tumors defined by specific chimeric transcripts. N Engl J Meet. 1994:331:294-299.

15. Coindre JM. lmmunohistochemistry in the diagnosis of soft tissue tumours. Histopathology. 2003:43:1-16.

Raoulin Soulard, MD; Valère Claude, MD; Philippe Camparo, MD; Jean-Philippe Dufau, MD; Patrick Saint-Blancard, MD; Philippe Gros, MD

Accepted for publication August 25, 2004.

From the Laboratoire d'Anatomie Pathologique, Hôpital d'Instruction des Armées du Val-de Grâce, Paris, France.

The authors have no relevant financial interest in the products or companies described in this article.

Reprints: Raoulin Soulard, MD, Hôpital d'Instruction des Armées du Val-de Grâce, 74 Boulevard de Port-Royal, 75005 Paris, France (e-mail: cellule-suspecte@yahoo.fr).

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