Divergent differentiation in round-cell tumours of soft tissues: an interim appraisal

Morphometric evaluation and clinical correlations in pediatric malignant small round cell tumors

Aims:

Nuclear size increases in malignant tumors and reflects DNA content, ploidy and proliferation index. Present study investigated if the nuclear morphometry could differentiate histomorphologically similar paediatric malignant small round cell tumors on hematoxylin and eosin stained sections for diagnostics in a resource poor setting.

Settings and Design:

All the consecutive malignant pediatric tumors received in Pathology Department from other faculties of King George's Medical University and also those referred directly to Pathology Department from other hospitals of city/other cities during 3 years period were recorded.

Materials and Methods:

Morphometric analysis was done in 22 confirmed (by higher ancillary techniques) but histomorphologically difficult to differentiate round cell tumors. All sections were analyzed by cell images from six different areas, using Leica Q win 500 images software.

Results:

Nuclear measurements were obtained for retinoblastoma (RB) (nine cases), neuroblastoma (five cases), Wilms tumor (WT) (three cases), rhabdomyosarcoma (three cases), malignant hemangiopericytoma (one case) and non-Hodgkin lymphoma (one case). Among the RBs, maximum mean nuclear area percent (24.93) was seen in a case with nerve involvement and metastasis, followed by cases with only nerve involvement (21.60) and smallest area (16.57) was in non-nerve involving, nonmetastatic cases. All five cases of neuroblastoma had almost similar mean nuclear area percent (18.05-18.29). WT case with metastasis had higher nuclear area (21.25) than nonmetastatic (19.47). Amongst all the tumors, minimum value (14.93) was seen in malignant hemangiopericytoma.

Conclusion:

Morphometric evaluation in paediatric malignant round cell tumors have generated useful data, and needs further multicentric confirmation for implementation.

Malignant small round cell tumors

Malignant small round cell tumors are characterised by small, round, relatively undifferentiated cells. They generally include Ewing's sarcoma, peripheral neuroectodermal tumor, rhabdomyosarcoma, synovial sarcoma, non-Hodgkin's lymphoma, retinoblastoma, neuroblastoma, hepatoblastoma, and nephroblastoma or Wilms’ tumor. Other differential diagnoses of small round cell tumors include small cell osteogenic sarcoma, undifferentiated hepatoblastoma, granulocytic sarcoma, and intraabdominal desmoplastic small round cell tumor. Differential diagnosis of small round cell tumors is particularly difficult due to their undifferentiated or primitive character. Tumors that show good differentiation are generally easy to diagnose, but when a tumor is poorly differentiated, identification of the diagnostic, morphological features is difficult and therefore, no definitive diagnosis may be possible. As seen in several study reports, fine needle aspiration cytology (FNAC) has become an important modality of diagnosis for these tumors. The technique yields adequate numbers of dissociated, viable cells, making it ideally suitable for ancillary techniques. Typically, a multimodal approach is employed and the principal ancillary techniques that have been found to be useful in classification are immunohistochemistry and immunophenotyping by flow cytometry, reverse transcriptase polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), and electron microscopy. However, the recent characterization of chromosomal breakpoints and the corresponding genes involved in malignant small round cell tumors means that it is possible to use molecular genetic approaches for detection.

Role of immunocytochemistry and DNA flow cytometry in the fine-needle aspiration diagnosis of malignant small round-cell tumors

In the present study, DNA flow cytometry (FCM) and immunocytochemistry (ICC) with a selected panel of antibodies were performed on 51 cases of malignant tumors which were referred for fine-needle aspiration biopsy (FNAB) to our Department of Cytology for the last 2 yr. Twelve cases were diagnosed as neuroblastoma, 16 as Ewing's sarcoma, 2 as retinoblastoma, 5 as non-Hodgkin's lymphoma (NHL), 5 as rhabdomyosarcoma, 2 as peripheral neuroectodermal tumors (PNETs), and 8 as Wilms' tumor. Eleven of 12 neuroblastomas were diploid by FCM, and 1 was aneuploid, with an S-phase fraction (SPF) of 8.3%. Neuron-specific enolase (NSE) was negative in 3 and positive in 8 cases of neuroblastoma, whereas neuroblastoma marker was positive in 3/11. Sixteen of 17 Ewing's sarcomas were diploid, and 1 showed tetraploid aneuploidy, with an SPF of 10.06%. Eight of 13 Ewing's sarcomas were positive for Mic-2 gene product (Ewing's marker). All 5 NHL were positive for leukocyte-common antigen (LCA). Three of 5 rhabdomyosarcomas were diploid, and 2 cases showed aneuploidy. Rhabdomyosarcoma showed muscle-specific actin positivity in 4 and desmin positivity in 3 cases. All 3 cases of PNET were diploid and positive for the Mic-2 gene product, whereas NSE and vimentin were positive in 2 cases. Both cases of retinoblastoma were diploid. Immunostaining was noncontributory in 1 case, and the other showed positivity for the retinoblastoma gene product, NSE, and chromogranin. Seven of 8 Wilms' tumors were diploid, and 1 showed aneuploid, with an SPF of 11.13%. Seven of 8 Wilms' tumors were positive for cytokeratin (CK), 5 were positive for NSE, 6 were positive for epithelial membrane antigen (EMA), and 5 were positive for vimentin. FNAB diagnosis of malignant round-cell tumors is difficult only by light microscopy. Due to the availability of specific markers for subgrouping tumors, ICC has proved to be more useful these days, while DNA FCM has little diagnostic value, as most of them are diploid. Further ancillary studies, e.g., electron microscopy, image analysis, and other molecular investigations, are required to further categorize these tumors more precisely for better clinical management of these cases.

Clinicopathologic study of ectomesenchymomas from Intergroup Rhabdomyosarcoma Study Groups III and IV

Ectomesenchymomas (EM) are rare malignant neoplasms usually consisting of rhabdomyosarcoma (RMS) with a neural component. Only 21 cases have been previously reported. Here we extend the clinicopathologic spectrum of EM by describing our findings in 15 cases. Only 5 patients were infants; 10 were < or =3 years old and 5 were > or =6 years old. No male predilection was observed; 7 were female. The originating institutional diagnoses were; RMS (12), undifferentiated sarcoma (1), or EM (2), suggesting underdiagnosis of this entity. The primary tumor sites included external genital (5), pelvis/abdomen (6), head and neck (3), and extremity (1). The size of the primary neoplasm was usually > or =5 cm at diagnosis but dissemination only occurred in a minority. Local infiltration was not uncommon. These neoplasms were typically multilobate, thinly encapsulated, hemorrhagic, and necrotic. Light microscopic features were highly variable, but embryonal RMS with scattered or clustered ganglion cells, often in lacunae, was characteristic. In some cases, primitive neuroblastic or neuroectodermal areas were found and/or a component of alveolar RMS was seen. Focal anaplasia was occasionally observed. Mitotic activity appears higher than previously appreciated and some necrosis was invariably present. Electron microscopy was performed in 11 cases, which confirmed skeletal muscle +/- neural differentiation. Cytogenetic studies performed in five cases revealed no specific abnormality. Monoclonal neuron-specific enolase was the best marker of ganglion cells and primitive neural elements. MIC-2 (CD99) membrane expression was not definitively present in any of the six cases examined. A number of the above parameters appear to be of some prognostic significance, but overall, these neoplasms appear to have a similar outcome as would be predicted for their RMS element alone (exclusive of any neural component), with respect to the RMS subtype, age of the patient, and anatomic location of the neoplasm.

Ectomesenchymoma: one or two tumors? Case report and review of the literature

Ectomesenchymoma has not previously been reported in a patient with the cutaneous nevus syndrome. A case of perineal ectomesenchymoma is presented with unusual cytogenetic findings. The significance of these is discussed and the world literature reviewed. This is the first such case reported.

Paediatric rhabdomyosarcoma: MyoD1 demonstration in routinely processed tissue sections using wet heat pretreatment (pressure cooking) for antigen retrieval

AIMS

To investigate wet heat pretreatment (pressure cooking) as a means of antigen retrieval for demonstration of MyoD1 in paraffin wax embedded tissue.

METHODS

Routinely processed tissue sections of transmission electron microscope confirmed cases of rhabdomyosarcoma were stained immunohistochemically with the MyoD1 antibody. Antigen retrieval was achieved by wet heat pretreatment of the tissue sections.

RESULTS

MyoD1 was stained successfully in all seven cases. The protein was localised to nuclei and cytoplasm depending on the type of tumour cell.

CONCLUSIONS

Wet heat pretreatment for antigen retrieval from routinely processed tissue sections permits excellent subsequent immunostaining for MyoD1 in rhabdomyoblasts.

Extraskeletal Ewing's sarcoma of the parotid region: a case report with the detection of the tumour's immunophenotypical characteristics

A case report of a malignant small round cell tumour of the parotid region, with features of extraskeletal Ewing's sarcoma is presented. Besides its rare location in the soft tissues of the parotid area, the tumour expressed focal NSE and desmin immunoreactivity, indicative of multidirectional differentiation.