The term, “Small Blue Round Cell Tumours” (SBRCT) is a heterogeneous group of highly aggressive malignant neoplasms which are composed predominantly of small and monotonous undifferentiated cells with high nucleocytoplasmic ratios, relatively small-sized nuclei, and scant cytoplasm.[1] This group includes diverse malignancies of epithelial, haematolymphoid, neuroectodermal, and mesenchymal origin. Differential diagnosis of these SBRCTs is particularly difficult due to their undifferentiated nature. This group of SBRCTs includes Ewing’s Sarcoma, Primitive Neuroectodermal Tumour (PNET) or extra skeletal Ewing’s sarcoma, neuroblastoma (NB), rhabdomyosarcoma, desmoplastic small round cell tumour, Non-Hodgkin’s lymphoma, small-cell osteosarcoma, small cell carcinoma (either undifferentiated or neuroendocrine), olfactory neuroblastoma, mesenchymal chondrosarcoma, lymphoblastic leukaemia, and blastemal component of Wilms’ tumour. Their clinical presentations and treatment protocol are completely different but all these tumours have remarkable overlap in their histomorphology, thus making the accurate diagnosis very difficult.(1,2)The anatomical locations and the microscopic details of these tumours and other aspects of their clinical presentations have a strong bearing on the relative likelihood of their respective diagnoses, and their immunohistochemical analyses may be tailored according to such considerations. Several monoclonal antibodies have been developed, that detect different epitopes of the antigens which are present in the tumour cells. However, there is no antibody which is specific for a single tumour type in the category of SBRCT. Despite recent advances in immunohistochemistry and molecular pathology, some cases of small-round-cell tumours of childhood remain diagnostically problematic.

The Retrospective and prospective study of paediatric neoplasm was conducted over time span of 10 years from 2012 to 2022 evaluated a total of 586 cases of paediatric tumours, including patients of 0–12 years of age group; attending the out patients and in patients department of Paediatrics and Paediatric Surgery at Jawaharlal Nehru Medical College, AMU, Aligarh, with the complaints of tumour or tumour associated sign and symptoms. Clinical profile of the Patients with radiological imaging data were collected histopathological examination of tissue sections along with relevant immunohistochemical analysis were implicated to attain a conclusive diagnosis. The profile of childhood small round blue cell tumours were studied focusing on the site of involvement, age and sex and clinicopathological findings. The material for this study was obtained from fresh sections of paraffin blocks of different cases which were stained with H and E stains, and relevant special stain along with the immunohistochemical stains. The cases were diagnosed and categorized according to the most recent WHO classification prevailing at the time of diagnosis.

Diagnosis was mainly established by amalgamating symptomatology at presentation, finding of radiological imaging, and histopathological examination and the panel of immunohistochemical markers. Out of 586 paediatric tumour cases, 316 (54%) cases were benign and 270 (46%) cases were malignant. Small round blue cell tumours (SRBCTs) comprised of 65 (11%) of the total cases, constituting of Ewing’s sarcoma 26 (40%) being the most frequently encountered SBRCT followed by Medulloblastoma 18 (27.7%) as second most common entity in this group, which were followed by Non-Hodgkin’s Lymphoma 6 (9.2%), Rhabdomyosarcoma 6 (9.2%), Neuroblastoma 5 (7.7%), Retinoblastoma 3 (4.6%) Desmoplastic Small Round Cell Tumour (DSRCT) 1 (1.5%) cases respectively [Figure 1a]. The mean age of the patients varied in different type of tumours, with lowest in medulloblastoma cases having mean in age of was 3.5 years while highest mean age were observed in cases of NHL being 12 years. No significant age preponderance were noticed in these tumour, except medulloblastoma which was found to be relatively higher in female children and lymphoma in males, however overall M: F ratio was found to be 2.3:1 [Figure 1b]. Ewings sarcoma were found in both skeletal and extra-skeletal sites including 1 case in paranasal sinus, NHL were mostly seen in cervical lymph nodes. Out of 5 cases of neuroblastoma 3 were olfactory involving nasal cavity and paranasal sinus while 2 were the cases of adrenal neuroblastoma and the case of DSRCT was reported in a 11 year old boy with liver mass. The clinical presentation of these tumour were mostly of site specific mass effect including pain, pathological fracture, vomiting, raised intracranial pressure, stuffy nose with nasal bleed and loss of vision respectively.

In developing countries like India, due to the lack of complete registration of newly diagnosed cases with local cancer registries, the exact burden of paediatric malignancies therefore goes unnoticed and is underestimated. Hospital based prevalence data, therefore, form the basis for estimating the tumour load. These data are essential for assessing geographical differences in the molecular and genetic profiles of these malignancies and also play a crucial role in ascertaining the required health care infrastructure in the management of childhood malignancies including malignant small round blue cell tumour. Malignant Small Round Blue Cell Tumours (SRBCT) are undifferentiated neoplasms, sharing an overlapping morphological pattern of small round blue cells. The family of tumours belonging to the group of SRBCT are characterised by high cellularity, small cell size, and a diffuse pattern of growth. The tumour cells have darkly staining nuclei and scanty cytoplasm, which gives an overall blue appearance in the haematoxylin and eosin (H&E) stained sections. The tumour cells are seen as round, slightly larger, or double the size of red blood cells in air-dried smears. [1-3] A panel of antibodies that recognise several tumour-associated markers is used for differential diagnosis. These constitute neuron-specific enolase and GD2 present in NB and, sporadically, in osteosarcomas and rhabdomyosarcomas; CD99 expressed by Ewing’s sarcoma and sometimes by PNETs; and desmin and cytokeratin present in desmoplastic tumours.[4] In the chromosomal study, the tumour typically shows a recurrent chromosomal translocation.[5] This stems from the fact that these tumours share not only similar morphological features, but also some immunophenotypic characteristics, thus requiring a broad panel of antibodies, which might not be included in the most basic immunohistochemistry panels, used in the routine work of most pathology laboratories. Furthermore, one should note that the diagnosis, prognosis, and/or therapeutic decision are often dependent on the knowledge of the existence of specific molecular alterations, which requires access to sophisticated molecular ancillary techniques. Of all 65 cases of Small round blue cell tumours (SRBCTs), entities observed in our study were Ewing’s sarcoma, Non-Hodgkin’s Lymphoma, Neuroblastoma, Medulloblastoma, Desmoplastic Small Round Cell tumour, Rhabdomyosarcoma and Retinoblastoma, quite similar to the observations made by Ezejiofor IF, et al. (6) Ewing’s sarcoma being the most frequently encountered entity constituted 40% of all the diagnosed cases of malignant SRBCT. They were mainly found to be involving the extremities similar with Obata et al., Oksüz et al. (7,8) while a 4 cases were of extra skeletal Ewings of which one case was diagnosed in paranasal sinus. The mean age being 11.8 years which was comparable with findings of Nazeer, et al. (9) Microscopically showed sheets and island of tumour cells with uniform round nuclei and scant cytoplasm, showing diffuse membranous positivity for CD99 and FLI1 nuclear positivity [Figure 2 a, b,c]. All the 18 cases of Medulloblastoma, a high grade CNS embryonal tumour (WHO Grade 4), presented with headache, nausea and vomiting due to raised intracranial pressure as a result of 4th ventricular obstruction. All the tumour showed sheets of undifferentiated cells with variable nuclear pleomorphism, high N:C ratio, while the Homer Wright rosettes were noticed in classical subtype [Figure 3a, b]and cell wrapping and high mitotic counts were mostly seen in large cell anaplastic cases. Other subtypes included desmoplastic nodular and MBEN (Medulloblastoma with extensive nodules). The tumour cells showed variable Synaptophysin [Figure 3c] and NSE positivity. Though histological subtyping was done amongst all the reported cases of medulloblastoma, however molecular stratification of these tumour as done in earlier studies done by Ellison DW et, al. (10) was not possible owing to lack of IHC surrogate markers ß-catenin, GAB1, YAP1 and OTX2 at our institute. Lymphoblastic lymphoma and Embryonal Rhabdomyosarcoma constituted the third common entity 6 (9.2%) cases in both these group. Slight male preponderance was noticed in lymphoblastic lymphoma cases. 4 cases were of T-lymphoblastic lymphoma that showed positivity for CD3 +, TDT+, CD 45, CD10+ (3 case), while immunophenotyping of 2 cases of B-lymphoblastic lymphoma was done by applying CD 45, CD20, CD79a relatable to the observations made by Derqaoui S, et al. (11) 3 cases of embryonal rhabdomyosarcomas were found in head and neck region including orbit while 2 in lower extremity and 1 as bladder mass. On microscopy tumour cells were arranged in sheets and ill-defined fascicles composed of tumor cells arranged in sheets of undifferentiated cells having small round to ovoid nuclie with fine to coarse chromatin, and inconspicuous nucleoli. The fibrous stroma showed variable vascularity with focal myxoid and hyaline changes. Confirmation of all the cases of ERMS were done using desmin, myogenin and MyoD1, of which desmin and myogenin showed strong diffuse positivity in almost all the tumors while MyoD1 exhibited weak expression, varying with result observed by Rekhi B, et al. (12) Of all 5 cases of neuroblastoma 3 were olfactory involving nasal cavity and paranasal sinus while 2 were the cases of adrenal neuroblastoma in patients of 5 and 8 years respectively presented with retroperitoneal mass and of which 1 case of adrenal neuroblastoma had metastatic lesion in the bone marrow alike the findings of Brodeur GM, et al.(13) All these cases were classified according to International Neuroblastoma Pathology Classification System (INPC)(14), 1 case of adrenal neuroblstoma was poorly differentiated while 1 was undifferentiated. 2 of the 3 cases of olfactory neuroblastoma were of differentiating type while 1 was poorly differentiated. Synaptophysin and NSE showed variable positivity in tumour cells while S100 helped highlighting the sustentacular cells thus confirming the diagnosis even in the poorly and undifferentiated subtypes. Retinoblastoma a primary intraocular malignancy of children, poses a significant challenge, in developing countries like India because of delayed diagnosis, advanced presentation, and incomplete treatment, often attributed to a lack of education and poor health seeking behaviour. Retinoblastoma accounted for 4.6% of all the 65 cases, and 1 case presented with leukocoria 2 cases presented with proptosis an advanced clinical presentation similar to what has been reported by Yahaya JJ, et al.(15) the classic histmorphological features included presence of monomorphic small, round blue cells with variable presence of homer wright and flexner wintersteiner rosettes [Figure 4a] depending on the degree of differentiation, prominent perivascular cuff of viable tumour cells were also noted along with foci of necrosis, calcification. These tumours showed strong cytoplasmic positivity for synaptophysin and NSE [Figure 4b, c], as proven by previous studies on Retinoblastoma. Our study included only 1 case of DSRCT, presenting as palpable abdominal mass with localised pain in 12 year boy, microscopically the biopsy tissue revealed Well defined nests of small round cells separated by desmoplastic stroma. IHC panel was observed to be quiet coinciding with the observation made by Costa MS included diffuse desmin and pan- cytokeratin positivity though synaptophysin and NSE showed slightly week positivity while chromogranin was completely negative. The IHC panel was helpful in distinguishing DSRCT from neuroendocrine tumour

The population based studies are required to study the demographics and to determine the burden of malignancies among paediatric patients in India. Hospital based studies have a major role to play in estimating the disease load in a particular geographical region and subsequent planning of health care infrastructure toward the disease. Stepwise algorithmic approach with inclusion of immunohistochemical panel of markers and molecular cytogenetic studies are required to differentiate amongst various SRBCTs and to reach a conclusive diagnosis in order to foster effective management of paediatric small round cell tumours.

1. D’Cruze L, Dutta R, Rao S, R A, Varadarajan S, Kuruvilla S. The role of immunohistochemistry in the analysis of the spectrum of small round cell tumours at a tertiary care centre. J Clin Diagn Res. 2013;7:1377-82 2. Nikitakis NG, Salama AR, O’Malley BW Jr, Ord RA, Papadimitriou JC. Malignant peripheral primitive neuroectodermal tumor-peripheral neuroepithelioma of the head and neck: A clinicopathologic study of five cases and review of the literature. Head Neck. 2003;25:488-98. 3. Sharma S, Kamala R, Nair D, Ragavendra TR, Mhatre S, Sabharwal R, et al. Round cell tumors: Classification and immunohistochemistry. Indian J Med Paediatr Oncol. 2017;38:349-53 4. Gregorio A, Corrias MV, Castriconi R, Dondero A, Mosconi M, Gambini C, et al. Small round blue cell tumours: diagnostic and prognostic usefulness of the expression of B7-H3 surface molecule. Histopathology. 2008;53:73-80. 5. Lee JH, Seo JH, Park KH, Jun BC. A case of malignant small round cell tumor of temporal bone with facial paralysis. Korean J Audiol. 2012;16:145-7 6. Ezejiofor IF, Adelusola K, Durosinmi MA, Leoncini L, Odesanmi WO, Ambrosio MR, et al. Immunohistochemical characterization of small round blue cell tumors of childhood at Ile-Ife, Nigeria: A 10-Year retrospective study. Arch Med Health Sci 2018;6:64-9. 7. Obata H, Ueda T, Kawai A, Ishii T, Ozaki T, Abe S, et al. Clinical outcome of patients with Ewing sarcoma family of tumors of bone in Japan: The Japanese Musculoskeletal Oncology Group cooperative study. Cancer 2007;109:767 75. 8. Oksüz DC, Tural D, Dincbas FÖ, Dervisoglu S, Turna H, Hiz M, et al. Non metastatic Ewing’s sarcoma family of tumours of bone in adolescents and adults: Prognostic factors and clinical outcome single institution results. Tumori 2014;100:452 8. 9. Nazeer A, Kandil A, Zahra O, Soliman M. Clinicopathological features and treatment outcomes in Ewing's sarcoma patients: A 10-year experience of Alexandria clinical oncology department. Indian J Med Paediatr Oncol 2017;38:316-20. 10. Ellison DW, Dalton J, Kocak M, Nicholson SL, Fraga C, Neale G, Kenney AM, Brat DJ, Perry A, Yong WH, Taylor RE, Bailey S, Clifford SC, Gilbertson RJ. Medulloblastoma: clinicopathological correlates of SHH, WNT, and non-SHH/WNT molecular subgroups. Acta Neuropathol. 2011 Mar;121(3):381-96. 11. Derqaoui S, Boujida I, Marbouh O, Rouas L, Hessissen L, Lamalmi N. Non Hodgkin Lymphoma Among Children: Pathological Aspects and Diagnostic Challenges. Clin Pathol. 2022 Apr 17;15:2632010X221090156. doi: 10.1177/2632010X221090156. PMID: 35465133; PMCID: PMC9019377. 12. Rekhi B, Gupta C, Chinnaswamy G, Qureshi S, Vora T, Khanna N, Laskar S. Clinicopathologic features of 300 rhabdomyosarcomas with emphasis upon differential expression of skeletal muscle specific markers in the various subtypes: A single institutional experience. Ann Diagn Pathol. 2018 Oct;36:50. 13. Brodeur GM, Hogarty MD, Mosse YP, et al. In: Pizzo PA, Poplack DG, eds. Principles and practice of pediatric oncology.6thed. Philadelphia: Williams and Wilkins; 2011. pp. 886-922. 14. Shimada H, Ambros IM, Dehner LP, Hata J, Joshi VV, Roald B. The International Neuroblastoma Pathology Classification (the Shimada system). Cancer. 1999;86:364-372. 15. Yahaya JJ, Rugwizangoga B, Mremi A, Munema A. Clinicopathological Findings of Retinoblastoma: A 10-Year Experience from a Tertiary Hospital in Kampala, Uganda. J Ophthalmol. 2019 Jun 16;2019:5829284. doi: 10.1155/2019/5829284. PMID: 31316824; PMCID: PMC6604297. 16. Costa MS, Lourenço SP, Guimarães MF, Nora MCMetastasized Intraabdominal Desmoplastic Small Round Cell Tumor.JCR 2019;9:265-269.