Figure 7.

a-f: Sheets of uniform and densely packed small cells showing round nuclei with finely granular nuclear chromatin (Haematoxylin and Eosin, a 200×, b 400×) and lack of reticulin fibres (Novotny reticulin stain, c 400×). The proliferation index is high (approximately 80% of cells showing immunoreactivity against MIB1, d 400×) and tumour cells demonstrate strong positivity for CD99 (e 630×). FISH analysis using an EWSR1(22q12) dual colour break apart rearrangement probe demonstrates tumour cells with separate orange and green signals indicating t(11;22)(q24;q12) (f 630×).