| Differential diagnosis |
Cytomorphological differentiating features |
Useful Immunocytochemistry/immunohistochemistry markers |
| Small cell carcinoma |
Round to oval cells with high N:C ratio, hyperchromasia, finely dispersed chromatin, no distinct nucleoli, and minimal cytoplasm. Molding, crushing, high mitotic rate. |
Synaptophysin, chromogranin, ki-67>30% |
| Carcinoid |
Monomorphic small round/elongated or plasmacytoid tumor cells arranged in loose groups or singly dispersed, sometimes around branching capillaries, rosette-like structures. Smooth nuclear contour, with salt and pepper chromatin and a small nucleolus; no or rare mitoses. Absence of molding, necrosis, or nuclear crushing. |
Synaptophysin, chromogranin, CK AE1/AE3 |
| Monophasic synovial sarcoma |
Cellular and shows a pericapillary arrangement of oval to round cells along with the presence of mast cells. The cells are highly pleomorphic compared to SFT. |
EMA/cytokeratin, TLE1 |
| SFT |
Low to moderate cellularity. Oval to elongate, rounded, or stellate cells with wispy cytoplasm. Intercellular ropy collagenous matrix. |
STAT 6 (nuclear positivity), CD34, Bcl2 |
| Sarcomatoid mesothelioma |
Loosely cohesive sheets of obviously malignant spindle cells. Poorly cellular smears of atypical spindle cells with a few fragments of collagen strands. |
D2-20, calretinin, CK AE1/AE3 |
| Inflammatory myofibroblastic tumor |
Hypocellular smears with several small clusters of spindle cells with bland nuclei, small nucleoli, and occasional myxoid matrix. Prominent inflammatory component composed of lymphocytes and plasma cells. |
ALK |
| Malignant peripheral nerve sheath tumor |
Highly cellular, single as well as syncytial and three-dimensional clusters. |
S100 |
| Fibromatosis |
Bland spindle cells with elongated nuclei embedded in metachromatic matrix material. |
SMA, beta-catenin (nuclear expression), cyclin D1 |
