Question 1:
A previously healthy 12-year-old female presented with an enlarging mass on the right posterior thigh. A 4 x 5 cm tumor was palpable superior to the popliteal fossa of the right leg with no overlying skin changes. The tumor cells demonstrate nuclear labeling with TLE1 immunohistochemical studies. The histology is shown in Figures 1-4.
Figure 1. H&E 40x
Figure 2. H&E 100x
Figure 3. H&E 200x
Figure 4 H&E 400x
Which of the following is the best diagnosis?