YALE JOURNAL OF BIOLOGY AND MEDICINE 74 (2001), pp. 13-20.Copyright C 2001. All rights reserved.

CASE REPORT

Intra-Abdominal Desmoplastic Small RoundCell Tumorc

Jaimie D. Nathana, Cynthia Gingalewski, and Ronald R. SalemDepartment of Surgery, Yale University School of Medicine, New Haven, Connecticut

Background: Intra-abdominal desmoplastic small round cell tumor is a rare malignancy with apredilection for young males. Unique histological and immunocytochemicalfeatures distinguish thetumorfrom other members of the family of small round cell tumors of infancy and childhood. Theaggressive nature oftumor spread, relative insensitivity to chemotherapy, and generally incompleteresectability result in a very poor prognosis. The authors report a case of a 39-year-old man withdiffuse abdominal and pelvic involvement of intra-abdominal desmoplastic small round cell tumortreated with aggressive chemotherapy and surgery.

Methods: Computed tomography (CT)-guided biopsy of an omental mass was performed.Histologically, discrete nests of uniform closely packed malignant cells were distributed in a back-ground offocally desmoplastic stroma. Immunocytochemistry demonstrated positivityfor epithelial,mesenchymal, and neural markers. On the basis of these unique histological and immunohisto-chemical characteristics, the diagnosis of desmoplastic small round cell tumor was made. Thepatient was treated with aggressive neoadjuvant chemotherapy consisting of a high-dose alkylator-based combination regimen, followed by surgery.

Results: The patient had a 10 to 15 percent regression in tumor mass in response to chemotherapy.Laparotomy revealed two large omental masses, another large mass adherent to the left colon andpelvic sidewall, and diaphragmatic, peritoneal and mesenteric studding with small nodules.Complete surgical resection was not possible.

Conclusions: Intra-abdominal desmoplastic small round cell tumor remains an aggressive malig-nancy with an extremely poor prognosis. Although some response to chemotherapy may be possi-ble, complete resection is rare, and surgical efforts are generally palliative.

INTRODUCTION

First described in 1987 by Sesterhennet al. [1], intra-abdominal desmoplasticsmall round cell tumor (IADSRCT)b is a

distinct variant of the small round celltumors of infancy and childhood. It is anuncommon, highly aggressive tumor witha predilection for young males [2-15].Predominantly intra-abdominal in location,

a To whom all correspondence should be addressed: Jaimie D. Nathan, M.D., Departmentof Surgery, Duke University Medical Center, PO. Box 3494, Durham, NC 27710; Tel.: 919-684-81 1 1; Fax: 919-681-7934; E-mail: nathaOO2@?mc.duke.edu.b Abbreviations: IADSRCT, intra-abdominal desmoplastic small round cell tumor; CT, com-puted tomography; EMA, epithelial membrane antigen; NSE, neuron-specific enolase;EWS, Ewing's sarcoma gene; WT1, Wilms' tumor suppressor gene.Submitted: April 6, 1999; Accepted: November 27, 1999.CThis article was originally published in Volume 72 of this journal in an incomplete form. Asa courtesy to the authors, we are re-publishing a corrected version of the article.

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14 Nathan et al.: Intra-abdominal small cell tumor

IADSRCT lacks a visceral site of originand spreads diffusely along serosal sur-faces. Histologically, this tumor is charac-terized by well-demarcated nests of tumorcells surrounded by an abundant desmo-plastic stroma. Co-expression of epithelial,mesenchymal and neural markers is aunique feature of IADSRCT [2-6, 9, 16],as is its association with a characteristicchromosomal translocation t(1 1; 12)(pl3;qll.2 or q12) [17-20]. Prognosis isuniformly poor because the malignancy isrelatively insensitive to chemotherapy andradiation, and surgical excision is rarelycomplete. Due to the rarity of this malig-nancy, optimal treatment regimens haveyet to be defined. We report the case of a39-year-old man with diffuse abdominaland pelvic involvement of intra-abdominaldesmoplastic small round cell tumor treat-ed with aggressive neoadjuvantchemotherapy and surgery.

CASE HISTORY

A 39-year-old white man, previouslywell, presented to his primary care physi-cian with a six-week history of left lower

quadrant abdominal discomfort, early sati-ety, increasing abdominal girth, rectalpressure during bowel movements,decreased caliber of bowel movements,intermittent night sweats and lower backdiscomfort, as well as a 12-pound weightloss.

On physical examination, theabdomen was moderately distended withascites, and two large, firm, nontender,mobile masses were palpable in bothlower abdominal quadrants. Laboratorystudies were unremarkable except for lac-tate dehydrogenase 287 u/l (normal 50-240 u/l). Computed tomography (CT)scan revealed an extensive soft tissuemass filling the pelvis and displacing therectum posteriorly, as well as severeascites and evidence of peritoneal carcino-matosis with multiple large solid massesinvolving the omentum and the bowelwall (Figure 1). CT-guided biopsy of anomental mass was consistent with desmo-plastic small round cell tumor.

Neoadjuvant chemotherapy was be-gun with intravenous cyclophosphamide,doxorubicin, and vincristine, alternatingwith ifosfamide and etoposide. The patientresponded clinically to the first three

* --j ij Figure 1. Pre-chemotherapycontrast-enhanced CT scanof the abdomen. Large bulkyintraperitoneal soft tissuemasses (M) are noted displac-ing bowel loops. Severeascites (A) and peritoneal nod-ules (arrows) are also evident.

Nathan et al.: Intra-abdominal small cell tumor 15

cycles of chemotherapy, requiring para-centesis less frequently. Subsequent CTscan revealed a 10 to 15 percent regressionin tumor mass. The patient underwent twoadditional courses of chemotherapy afterwhich he required stem cell rescue. CTscan showed no further change in tumormass.

At laparotomy, 2.5 liters of asciteswas found within the peritoneal cavity.Two large mobile masses were foundattached to the greater omentum, withtumor very closely adherent to the splenicflexure. A third large mass was attached tothe left pelvic sidewall and to the sigmoidcolon and extended between the bladderand the rectum. The diaphragm was stud-ded with small nodules, and tumor noduleswere noted throughout the mesentery andparietal peritoneum. The tumor was mobi-lized from the splenic flexure and from thesigmoid colon, bladder and rectum andwas transected at its attachment to the leftpelvic side wall, allowing en bloc resec-tion of the three masses and the omentum.The parietal peritoneum was removedwith electrocautery, and the nodules with-in the small bowel mesentery were maxi-mally resected. Post-operative course hasbeen uneventful, and subsequent therapeu-tic efforts will include radiation and fur-ther chemotherapy.

PATHOLOGY

Macroscopic findings

The 2,000-gm specimen consisted ofomentum studded with numerous tumornodules of variable size, some distinct andspherical and others confluent. The speci-men measured 20 cm x 20 cm x 11 cm asa whole, with tumor nodules ranging from0.5 cm to 16 cm in size. The tumor wasfirm and smooth, and the cut surface of thenodules revealed firm, white densely

fibrotic areas alternating with soft, gelati-nous myxoid areas.

Histological findings

The specimen obtained by CT-guidedbiopsy was characterized by discrete nestsof uniform closely packed malignant cellsdistributed in a background of focallydesmoplastic stroma (Figure 2). The nestsof cells varied in appearance from irregu-lar islands to narrow cords and infiltratingstrands. The tumor cells were small, withhyperchromatic round to oval nuclei, scanteosinophilic cytoplasm and indistinctcytoplasmic borders. Nucleoli were gener-ally inconspicuous. Mitotic figures wererare, and anaplastic nuclei were not pre-sent. Tubular or glandular foci, rosettes, orother recognizable signs of differentiationwere absent. The stroma was dense andcollagenous with occasional scatteredspindle-shaped fibroblast-like cells. Thetumor predominantly consisted of malig-nant cells, with the stromal componentoccupying a smaller portion of the speci-men. In addition to the characteristics ofthe biopsy specimen, the resected speci-men revealed cystic changes and somemyxoid areas within the stroma.

Immunohistochemistry

On immunohistochemical staining,the neoplastic cells were strongly positivefor the epithelial marker keratin (AEl/AE3and CAM 5.2), diff-usely throughout thecytoplasm. Although positivity for epithe-lial membrane antigen (EMA) was alsostrong, its distribution was more patchythan that of keratin. Reactions with anti-vimentin antibody revealed diffuse cyto-plasmic positivity in the majority of tumorcells, while staining with desmin was spo-radically positive and showed a paranu-clear cytoplasmic "dot-like" or "globoid"pattern of expression. The tumor cellsdemonstrated focal positivity for alpha-

16 Nathan et al.: Intra-abdominal small cell tumor

smooth muscle actin (Figure 3). Stainingfor neuron-specific enolase (NSE) and S-100 protein, markers of neural differentia-tion, exhibited a focal pattern of positivity(Figure 4).

DISCUSSION

IADSRCT is a recently describedentity belonging to the category of smallround cell tumors of infancy and child-hood, including Ewing's sarcoma, primi-tive neuroectodermal tumor, embryonal oralveolar rhabdomyosarcoma, neuroblas-toma, malignant lymphoma, Askin'stumor, and rhabdoid tumor. This group ofneoplasms is characterized by small uni-form cells with sparse cytoplasm, diffusegrowth pattern, and high cellularity.

Specific clinical, topographical, mor-phological and immunohistochemical fea-tures, however, differentiate IADSRCTfrom other members of its family.Although not as marked as reported in thefirst series of IADSRCT by Gerald et al. in1991 [3], the male predominance of thistumor has been described in several subse-quent reviews (male-to-female ratio,greater than 3:1) [8, 21-23]. Adolescentsand young adults are typically affected,with a mean age between 18 and 20 years(range 3 to 48) [23], and greater than 70percent of patients present before the ageof thirty in reviews of larger series [3, 21,22]. The most common presenting symp-toms ofIADSRCT are abdominal pain anddistention, related to enlarging tumor bur-den and sometimes to ascites, as in ourcase. The tumor tends to arise intra-abdominally on serosal surfaces withoutan obvious visceral primary site. A domi-nant omental or pelvic mass is commonwith multiple surrounding smaller satellitenodules adherent to the peritoneum.Grossly, the tumor is firm, smooth andbosselated, with a gray-white cut surface

and focal necrotic and hemorrhagicregions [2-4].

Histologically, IADSRCT is charac-terized by well-defined nests or strands ofuniform small round tumor cells surround-ed by an abundant desmoplastic stroma.Generally, morphologic signs of differen-tiation are absent. However, tubular lumi-na have been noted in pathologic speci-mens of IADSRCT [2], and glandular andneural components have, likewise, beenreported [4, 16, 21, 22]. Although themalignant cells and the stromal compo-nent usually occupy equal proportions ofthe tumor, the stroma in IADSRCT can behighly variable, with some tumors beingpredominantly cellular and others predom-inantly stromal [2, 21, 23]. Within thedense collagen-rich stroma, spindle cellsresembling fibroblasts or myofibroblastscan be identified. The stroma may consistof myxoid areas, cystic degeneration andcalcification [21]. In our case, the CT-guided biopsy specimen did not revealthese components, suggesting that themyxoid areas and cystic changes found inthe resected specimen may have beenassociated with the neoadjuvant chemo-therapy received. Alternatively, tumor het-erogeneity may account for the histologi-cal differences.

Although the clinical and histologicalfeatures of IADSRCT may be sufficientlydistinctive to suggest its diagnosis, IAD-SRCT is most easily distinguished fromother members of its family by the uniqueimmunoreactivity for epithelial, mes-enchymal and neural markers. Immuno-positivity for keratin and EMA, markers ofepithelial differentiation, is usually diffusethroughout the cytoplasm and widespread.Some reports have demonstrated, howev-er, that EMA reactivity is variable, withpatchy or scattered distribution and local-ization adjacent to the cytoplasmic mem-branes [6, 24]. The mesenchymal markers,vimentin and desmin, are consistentlyexpressed in IADSRCT. Vimentin usually

Nathan et al.: Intra-abdominal small cell tumor

Figure 2. Histologic appearanceof tumor. The tumor is composed ofirregular islands and cords of malig-nant cells that are oval and spindle-shaped with scanty cytoplasm anddark ovoid to round nuclei. Islandsand cords of tumor cells are sepa-rated by a dense desmoplastic stro-ma containing occasional spindle-shaped cells. (H & E, x 250).

Figure 3. Immunostaining forsmooth muscle actin. Focalcytoplasmic immunopositivity forSMA is present in many tumorcells. (Immunoperoxidase, x 400).

Figure 4. Immunostaining forS-100 protein. The tumor cellsshow focally positive cytoplas-mic immunohistochemicalstaining for S-100 protein, amarker of neural differentiation.(Immunoperoxidase, x 400).

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18 Nathan et al.: Intra-abdominal small cell tumor

exhibits widespread, diffuse cytoplasmicstaining, while desmin positivity has aclassic paranuclear "dot-like" or "globoid"pattern, though a diffuse, cytoplasmicquality has been noted [16, 22]. Despiteimmunoreactivity for keratin, EMA anddesmin, microscopic features of epithelialor myoid differentiation are generallyabsent. In our case, neoplastic cells werefocally positive for alpha-smooth muscleactin, an uncommonly expressed antigenin IADSRCT [22]. Although neurosecreto-ry dense-core granules, ultrastructural evi-dence of neuroendocrine differentiation,have been reported only rarely [3, 4, 16],IADSRCT is usually immunopositive forNSE and occasionally expresses S-100protein as well [16, 21, 25]. Co-expressionof epithelial, mesenchymal, and neuralantigens in the same cell suggests thatIADSRCT may arise during developmentfrom a primitive pluripotential stem cell.However, the histogenesis of IADSRCTremains unknown.

Evidence demonstrating the associa-tion of a specific chromosomal abnormali-ty with some cases of IADSRCT may pro-vide insight into the histogenesis of thistumor at a molecular level. In most casesanalyzed cytogenetically, the genetic alter-ation involves a unique reciprocal translo-cation, t(11;12)(pl3;qll.2 or q12), and isnot the same 11;12 translocation found inother small round cell tumors, giving fur-ther support to the notion that IADSRCT isa distinct, yet related, tumor type [17-20].The breakpoint loci involve the chromoso-mal regions of the Ewing's sarcoma gene(EWS) and the Wilms' tumor suppressorgene (WTI), which have been implicated inother malignant developmental neoplasms[26, 27]. Recent studies have demonstratedevidence of expression of chimeric EWS-WTI RNA in IADSRCT resulting from thefusion of the EWS and WTI genes [28]. Assuggested by Parkash et al. [29], the diver-gent differentiation of IADSRCT may bethe result of the EWS-WTI fusion, allowing

a combination of neural differentiation ofEwing's neoplasms with the multidirec-tional differentiation of Wilms' tumors.Although chromosomal analysis has beenconducted in only a small number of cases,the t(ll;12)(pl3;qll.2 or q12) appears to bea specific alteration and may prove usefulin the elucidation of the molecular patho-genesis of IADSRCT and perhaps in themolecular diagnosis of the tumor.

The diagnosis of IADSRCT is usuallynot made until tissue is obtained at laparo-tomy, thereby precluding the use of neoad-juvant therapy. In our case, diagnosis wasmade by CT-guided biopsy, with obvioustherapeutic consequences. In 1992,Setrakian et al. [30] described the case ofa 20-year-old man with a subhepatic softtissue mass biopsied by CT-guided fineneedle aspiration. Cytologic analysisrevealed small round cells with scarcecytoplasm and occasional fibroblast-likecells, and immunostaining was positive forcytokeratin, desmin and NSE, confirmingthe diagnosis of IADSRCT. The specifici-ty of immunopositivity for epithelial, mes-enchymal and neural markers makes CT-guided fine needle aspiration a very usefultechnique in the diagnosis of IADSRCT.

IADSRCT exhibits an extremelyaggressive clinical course and in general,carries a very poor prognosis. Although astandardized treatment protocol is lacking,several studies have attempted to definethe biological behavior of the tumor and itsresponse to various therapeutic modalities.In the series by Gerald et al. [3] in 1991, 19patients underwent surgical "debulking,"followed in most cases by multi-drugchemotherapy with or without irradiation.Generally, an incomplete surgical resec-tion and partial response to chemotherapywas followed by rapid, uncontrollablerelapse. In 1993, Ordonez et al. [22] like-wise reported only rare complete surgicalresection but initial tumor reduction withadjuvant multi-agent chemotherapy.Again, however, progressive tumor growth

Nathan et al.: Intra-abdominal small cell tumor 19

was the rule. With evidence in these stud-ies of some degree of chemosensitivity inthese tumors, Farhat et al. [31] describedfour patients with IADSRCT who weretreated with an adjuvant cisplatin-basedmulti-drug regimen following suboptimalsurgical debulking or biopsy. All fourpatients demonstrated stable disease afterfour to nine courses of chemotherapy. In aprospective study by Kushner et al. [9] in1996, five of eight previously untreatedpatients experienced complete remissionfollowing a high-dose neoadjuvant alkyla-tor-based regimen and surgical resection.Another two patients had complete surgi-cal resection at the time of diagnosis andwere in complete remission followingadjuvant chemotherapy. With or withoutconsolidative radiotherapy and/or mye-loablative chemotherapy, five of the sevenpatients remained in complete remission10 to 39 months from the start of the alky-lator-based regimen, demonstrating thatprogression-free survival of prolongedduration is attainable. In Amato et al. [7],four of five patients treated with variousmulti-agent chemotherapeutic regimenswith or without surgical intervention hadevidence of a partial response but eventu-ally died from their disease within 3.5years from diagnosis. Treated with a regi-men similar to that described by Kushneret al., our patient had an apparent clinicalresponse to therapy, but CT scan demon-strated only a 10 to 15 percent reduction intumor mass, and complete surgical resec-tion was not possible. Adjuvant therapywill include irradiation and additionalchemotherapy.

IADSRCT remains an aggressivemalignancy with an extremely poor prog-nosis. Although some response to chemo-therapy may be possible, in particular tohigh-dose alkylator-based regimens, com-plete surgical resection is rare, and despiteaggressive therapy, survival rates remainlow due to the refractory nature of thetumor. Additional studies are necessary to

further elucidate the biology of the diseaseand to optimize treatment regimens.

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