Fig. 1: Infantile fibrosarcoma involving the gastrointestinal tract (cases 1–4).

a Highly cellular proliferation of monomorphic spindle cells with eosinophilic cytoplasm and hyperchromatic ovoid nuclei (case 1). b Cellular proliferation of short spindled cells with abundant mitotic figures (44/10 HPF) (case 2). This tumor demonstrated locally aggressive growth, such that the patient died within 2 weeks of presentation. c Cellular fascicles of monomorphic spindle cells (case 3). d Cytologically bland spindle-cell proliferation in vaguely fascicular arrangement (case 4). e Spindle cells with inconspicuous cytoplasm with stromal and perivascular hyalinization (case 3). f Highly infiltrative proliferation of monomorphic spindle-cell dissecting through glands in the antral mucosa (case 3).