1. An 80-year-old female presented with an ulcerated nodule on the left cheek. An excision was performed.

2. The actual H&E slide will be presented as virtual microscopy. The following images are representative of the virtual image.

8. Based on the H&E findings on the skin excision, what is your differential diagnosis? List your 5 top choices. Once you have finished this section, you may not return to it

9. Atypical fibroxanthoma Basal cell carcinoma Large cell lymphoma Leiomyosarcoma Melanoma Metastatic carcinoma Metastatic sarcoma Pleomorphic fibroma Primary undifferentiated pleomorphic sarcoma Squamous cell carcinoma

10. Atypical fibroxanthoma Leiomyosarcoma Melanoma Primary undifferentiated pleomorphic sarcoma Squamous cell carcinoma Answers for Diff Dx

11. Based on the clinical history and your differential diagnosis, which immunostains would most likely be helpful in arriving at a definitive diagnosis? Please choose 3 stains. Once you have chosen, you cannot choose an additional panel of immunostains.

12. CD3 CD45 CD117 Cytokeratin CK7 CK20 Desmin Factor XIIIa GATA-3 MOC31 PAX5 PAX8 S-100 protein Vimentin

13. Answers for Stains Cytokeratin Desmin S-100

14. The following immunostains were performed

15. S-100 protein

16. Desmin

17. Cytokeratin

18. What is the best diagnosis? Squamous cell carcinoma