Abstract

Small round cell tumors (SRCTs) are a group of malignancies (non-Hodgkin lymphoma, neuroblastoma, retinoblastoma, hepatoblastoma, nephroblastoma, rhabdomyosarcoma, small cell anaplastic carcinoma, Ewing sarcomal peripheral neuroectodermal tumor, and desmoplastic small round cell tumor), characterized both cytologically and histologically by a predominantly small round to oval, and relatively undifferentiated cells. Together they form a formidable group and an overwhelming majority of childhood malignancies. The patients may present in later (inoperable) stage with huge intrathoracic and intraabdominal mass, when chemotherapy and/or radiation therapy may be the first or only line of treatment. As a less invasive procedure fine needle aspiration (FNA) cytology has definite advantage over surgical excision biopsy to arrive at a tissue diagnosis before initiation of therapy. Because of the morphologic similarities, the SRCTs may pose a differential diagnostic problem in the practice of clinical cytology, especially when they are poorly differentiated. Important cytomorphological features, which help in the identification of various SRCTs include completely dissociated cell population and lymphoglandular bodies (cytoplasmic fragments) in non-Hodgkin lymphoma (NHL), eosinophilicfibrillar material and Homer-Wright rosettes along with cellular processes in neuroblastoma, acinar formation in hepatoblastoma, blastema cells with tubular differentiation in nephroblastoma, tadpole shaped cells in embryonal rhabdomyosarcoma, extreme nuclear molding and perinuclear blue inclusion in small cell anaplastic carcinoma (SCAC), irregular, punched out and large cytoplasmic vacuolations due to glycogen in Ewing sarcoma, and sheets of undifferentiated small round cells surrounded by collageneous stroma in desmoplastic small round cell tumor (DSRCT). Some of these features such as nuclear molding, rosette, and acinar formation are noticed in more than one type of SRCTs. Moreover, the characteristic cytomorphological features may be present in 70-80% cases and for categorization of the remaining cases, contribution from ancillary studies is essential. It is suggested that cytomorphological features along with one or more of the parameters such as special stains (cytochemistry), immunocytochemistry (ICC), electron microscopy (EM), tissue culture, DNA ploidy, karyotype and molecular analysis can increase the diagnostic accuracy of SRCTs. However, these facilities may not be available in all the laboratories, especially in the developing countries, and even if available in a limited form, a tissue diagnosis has to be offered often by FNA cytology based on morphological features, as a life saving measure in seriously ill patients before the results of ancillary studies are finalized.