Chapter 7 Diagnostic Dilemmas in FNAC Cytology: Small Round Cell Tumours 7 Contents The term small round-cell tumour (SRCT) is a generic term for tumours composed of malignant 7.1 Small Round Cell Tumours of Childhood . 133 round cells that are slightly larger or double the 7.1.1 Ewing’s Sarcoma/Primitive size of red blood cells in air-dried smears or Neuroectodermal Tumour.................134 7.1.2 Neuroblastoma ..........................136 measure less than 10 μm in diameter in alcohol- 7.1.3 Ganglioneuroblastomas ...................136 fixed smears, and have scanty cytoplasm. Their 7.1.4 Rhabdomyosarcoma......................137 features, including cellularity, morphology, pat- 7.1.5 Acute Lymphoblastic Leukaemia and LBL . 139 tern of cell arrangement and smear background, 7.1.6 Small Round Cell Tumours of Kidney.......141 often pose a diagnostic challenge in FNAC since 7.1.7 Hepatoblastoma .........................141 7.1.8 Pleuropulmonary Blastoma................142 similar features may reflect a variety of tumour 7.1.9 Small-Cell Synovial Sarcoma...............142 types and subtypes. Within the group of tumours that express a dominant or occasional SRCT (ex- 7.2 Small Round Cell Tumours in Adults ......142 cluding the central nervous system neoplasms) 7.2.1 Desmoplastic Small Round Cell Tumour ....143 include Ewing‘s sarcoma and primitive neuro- 7.2.2 Small-Cell Carcinoma of the Lung..........144 ectodermal tumour (PNET; ES/PNET) and its 7.2.3 Burkitt’s Lymphoma . 144 7.2.4 Lymphoglandular Bodies..................145 variants, neuroblastoma, desmoplastic SRCT, 7.2.5 Merkel Cell Carcinoma ...................146 rhabdomyosarcoma (RMS) (alveolar, solid and 7.2.6 Olfactory Neuroblastoma .................147 embryonal), small-cell osteosarcoma, chondro- sarcoma (myxoid and mesenchymal), round-cell References ....................................148 and myxoid liposarcoma, synovial sarcoma (mo- nophasic undifferentiated), primitive malignant peripheral nerve sheath tumour (malignant small-cell schwannoma), Non Hodgkin lym- phome (NHL), Merkel cell tumour of the skin and small-cell carcinoma including neuroendo- crine carcinoma [1]. 7.1 Small Round Cell Tumours of Childhood Tumours of infancy and childhood are most commonly referred to as the SRCT group and include ES/PNET, neuroblastoma, RMS and ma- lignant lymphoma. Other malignancies that may be considered in the differential diagnosis include small-cell osteogenic sarcoma, undifferentiated (anaplastic) hepatoblastoma, granulocytic sarco- 134 ma, blastemal-type Wilms‘ tumour, and desmo- nucleoli and scant, but almost always present, plastic small-cell tumour of the peritoneum [2]. perinuclear clear cytoplasm, suggesting epithe- Although challenging, FNAC of childhood SRCT lial differentiation (Fig. 7.1). Cells are arranged can be diagnostic in the majority of cases, allow- singly or in cohesive clusters. Homer-Wright ing specific therapy to be given to patients with rosettes may be seen and there are no ganglion unresectable SRCT without a tissue biopsy as cells or neuropil. There is an absence of frequent well as documenting recurrent and/or metasta- mitotic figures, large nucleoli, nuclear pleomor- tic disease [2]. SRCTs usually have characteristic phism, cellular debris, histiocytes and polymor- cytomorphology. However, when these tumours phonuclear leukocytes [6]. Smears appear clean, are undifferentiated, morphological criteria may with small, uniform cells having features sugge- not be sufficient to arrive at a correct diagnosis. sting a neuroendocrine epithelial tumour (Fig. A variety of ancillary studies including electron 7.2). As regards the differentiation of Ewing’s microscopy, immunohistochemistry, DNA ploi- sarcoma, a few subtle differentiating features can dy, cytogenetics and FISH may provide valuable be observed: the cells in Ewing’s sarcoma have a additional information for the precise characte- finer nuclear chromatin in comparison to those 7 risation of these neoplasms. Some ancillary stu- of PNET tumour, and punched-out clear cyto- dies may also be used for assigning these cases to plasmic vacuoles are present. PNET shows nu- prognostically significantsubgroups, helping to clear moulding, unipolar cytoplasmic tags and define the most suitable chemotherapeutic regi- Homer-Wright rosettes [7]. mens. Since most of these special studies require only a small amount of cellular material, FNAC is ideally suited for obtaining samples for these procedures [3]. 7.1.1 Ewing’s Sarcoma/Primitive Neuroectodermal Tumour ES/PNET is a family of malignant SRCTs that ex- hibits neuroepithelial differentiation, most often presenting as a soft-tissue or bone lesion in the trunk or axial skeleton, predominantly in older children and adolescents. Isolated cases of PNET have been observed in FNAC samples from vis- ceral sites such as the ovary, testis, uterus, blad- der, pancreas and kidney [4]. In some cases the primary diagnosis made by FNAC enables the paediatric oncologist to give specific therapy for the otherwise unresectable tumour and thus achieve remission [5]. Local recurrences may include the chest wall, pleura and pericardium, whilst metastatic disease may be found almost anywhere. The cytological features of ES/PNET include malignant cells with a high N/C ratio, hyper- Fig. 7.1 chromatic nuclei without prominent nucleoli, FNAC bone lesion. Ewing’s sarcoma/primitive neuroec- distinctively smooth nuclear membrane con- todermal tumour (ES/PNET). a Low-power view revea- tour, finely granular chromatin, one or two small ling a small round-cell tumour (SRCT). b MGG stain. Small Round Cell Tumours tic Tumours Chapter 7 135 Fig. 7.1 Continued from previous page. c Pap stain. Cytological features include malignant cells with a high N/C ratio, hyperchromatic nuclei without prominent nucleoli, distinctively smooth nuclear membrane contour, finely granular chromatin, one or two small nucleoli and scant, but almost always present, perinuclear clear cytoplasm suggesting epithelial differentiation. Cells are arranged singly or in cohesive clusters. Homer-Wright rosettes may be seen and there are no ganglion cells or neuropil. There is an absence of frequent mitotic figures, large nucleoli, nuclear pleomor- phism, cellular debris, histiocytes and polymorphonu- clear leucocytes Fig. 7.2 FNAC thigh lesion. ES/PNET. (see next page) 136 7.1.2 Neuroblastoma Neuroblastoma is an SRCT that is characterised by rosettes and background filamentous/fibrillar material in FNAC material (Fig. 7.3) [10]. Cyto- logical features in conjunction with immunocy- tochemistry and electron microscopy performed on the FNAC material enable making a diagnosis of primary or metastatic neuroblastoma [10]. It is possible to use the Southern blotting technique to demonstrate N-myc amplification in material Fig. 7.2 obtained from FNAC [11]. N-myc amplification Continued from previous page. FNAC thigh lesion. ES/ by interphase FISH and immunocytochemistry PNET. a Smears appear clean, with small, uniform cells result in the molecular characterisation of neu- 7 having features suggesting a neuroendocrine epithelial roblastic tumours. Such analyses are of progno- tumour. b–d As regards the differentiation of Ewing’s stic significance because they predict tumour sarcoma, a few subtle differentiating features can be ob- served: the cells in Ewing’s sarcoma have a finer nuclear behaviour and response to therapy according to chromatin in comparison to those of the PNET tumour, International Neuroblastoma Staging System/In- and punched-out clear cytoplasmic vacuoles are present. ternational Neuroblastoma Risk Groups criteria PNET shows nuclear moulding, unipolar cytoplasmic [12]. Amplification of the transcription factor N- tags and Homer-Wright rosettes. e PAS stain shows myc is an important molecular diagnostic tool in strong positivity for cytoplasmic glycogen. f Strongly positive for synaptophysin. g Strongly positive for CD99. stratifying treatment for neuroblastoma [13]. Other small cell neoplasms, including rhabdomyosarco- ma (RMS), blastemal Wilms‘ tumour and lymphoblastic lymphoma (LBL) have also shown positivity, but the staining reactions are usually weak and focal Ancillary studies, including electron microscopy, immunocytochemistry and cytogenetics (t11;22) may be performed on FNAC material and thus exclude other SRCTs of childhood such as mali- gnant lymphoma and RMS. CD99 immunostai- ning and/or molecular studies, particularly in the intermediate and atypical variants, may help to establish a definitive FNAC diagnosis, thus avoiding an open surgical biopsy [8] (Fig. 7.2g). Fig. 7.3 Other small round cell neoplasms, including FNAC paraspinal mass. Neuroblastoma. Homer-Wright RMS, blastemal Wilms‘ tumour and lympho- rosette. blastic lymphoma (LBL) have also shown posi- tivity, but the staining reactions are usually weak and focal [9]. The differential diagnosis between 7.1.3 Ganglioneuroblastomas ES/PNET and neuroblastoma can be difficult ba- sed on the FNAC morphology alone, although morphological differences do exist. Clinical fea- Ganglioneuroblastomas show the characteristic tures (e.g. age, primary site, metastatic patterns), Homer-Wright rosettes, ganglion cells and fibril- catecholamine levels, electron microscopy and lary material [14]. cytogenetics are necessary to establish the cor- rect diagnosis (see 7.1.2). Small Round Cell Tumours tic Tumours Chapter 7 137 7.1.4 Rhabdomyosarcoma immunocytochemistry in the demonstration of desmin in FNAC is helpful in reaching a diagno- sis. RMS accounts