Table 1.

Common and rare, divergent cytologic features of SRCS

Tumor	Diagnostically important microscopic features	Divergent microscopic features
ES	Smears patterns and background: Hypercellular smears. Mixture of clustered and dispersed cells. Occasional perivascular arrangement of tumor cells and pseudorosettes. Tigroid background Tumor cells micromorphology: Monomorphous population of small round cells with high N:C ratio, bland nuclear morphology, and inconspicuous nucleoli. Double cell population large light and small dark cells (better appreciated in air-dried smears). Larger cells with cytoplasmic vacuoles that contain glycogen. Occasionally moderately pleomorphic cells, spindle-shaped cells, or cells with rhabdoid morphology	Desmoplasia (eosinophilic connective tissue) in the background. Intranuclear inclusions
CIC-rearranged sarcoma	Smears patterns and background: Hypercellular smears. Dispersed cells and loosely cohesive cell clusters and sheets. Perivascular arrangements and traversing capillaries evident in cell sheets. Necrotic debris and myxoid stroma Tumor cells micromorphology: Mild to moderate pleomorphism but more prominent variation in size and shape of nuclei, compared to that of ES. Centrally or eccentrically placed round-to-ovoid, occasional polygonal, angulated, and spindle-shaped nuclei with irregular nuclear membrane, coarse chromatin pattern and variably prominent nucleoli. Majority tumor cells with scant to moderate cytoplasm, occasionally small cytoplasmic vacuoles or poorly preserved cytoplasmic borders creating slender cytoplasmic processes connecting one cell to another	Desmoplasia (eosinophilic connective tissue) in the background and tigroid background. Cells with rhabdoid morphology
Sarcoma with BCOR genetic alterations	Smears patterns and background: Hypercellular smears with dispersed cells and loosely cohesive cell clusters. Sometimes perivascular arrangements, or papillary clusters with vascular cores. Desmoplasia (connective eosinophilic tissue), myxoid stroma, and necrotic debris Tumor cells micromorphology: Round and spindled cells with evident pleomorphism. Double cell population: large, “light” cells and small, dark cells resembling those of ES
DSRCT	Smears patterns and background: Moderate cellular smears. Loosely cohesive sheets and clusters or less common, tight clusters. Desmoplastic stroma fragments and occasional acinar-like structures or pseudorosettes. Necrosis and apoptosis Tumor cells micromorphology: Uniform or slightly pleomorphic undifferentiated cells with round-to-oval, slightly angulated, irregular nuclei with granular chromatin, inconspicuous nucleoli and scant cytoplasm. Nuclear molding and paranuclear cytoplasmic densities	Hint of myxoid background matrix
Poorly differentiated SS of small cell type	Smears patterns and background: Hypercellular smears. Mixture of tight clusters, sheets, dispersed small round cells and stripped nuclei. Rarely cells forming rosette-like structures Tumor cells micromorphology: Small round uniform cells. Showing round-to-ovoid nuclei, and scant cytoplasm. Occasional mild nuclear pleomorphism	Double cell population: large, light cells and small, dark cells resembling those of ES
Alveolar RMS	Smears patterns and background: Hypercellular smears. Dispersed cells admixed with naked nuclei and clusters of loosely cohesive cells. Sometimes perivascular arrangement of tumor cells and lacy (tigroid) background Tumor cells micromorphology: Predominantly small- to medium-sized round or ovoid cells with scanty cytoplasm, hyperchromatic nuclei with coarse chromatin, often with large nucleoli. Occasionally Binucleated and multinucleated tumor cells and cells with eccentric nuclei and cytoplasmic densities
Mesenchymal chondrosarcoma	Smears patterns and background: Predominantly cohesive cell clusters. Biphasic pattern. Fragments of fibrocartilaginous matrix and variable presentation of fibrillar and myxoid stroma and osteoclasts Tumor cells micromorphology: Tumor cells with sparse or moderate cytoplasm and round-to-oval, occasionally spindled nuclei with coarse chromatin and inconspicuous nucleoli	Desmoplasia (eosinophilic connective tissue) in the background
Small cell osteosarcoma	Smears patterns and background: Hypercellular aspirates. A mixture of cohesive fragments and dispersed small- to medium-sized cells. Rare osteoid Tumor cells micromorphology: Small- to medium- sized, slightly pleomorphic cells with high N:C ratios, round, occasionally oval or elongated nuclei, finely granular nuclear chromatin, scant cytoplasm or bare nuclei, fine cytoplasmic vacuoles	Chondromyxoid matrix