Figure 1. Histologic staining of the patient’s anal SCC tumor. The tumor stained positive for p16 in the squamous epithelium, indicating HPV infection. Hematoxylin and eosin (H&E) staining revealed a high degree of immune infiltration into the tumor. Immunohistochemistry stained positive for CD3, CD8, and CD4, indicating both cytotoxic and helper T cells are present in the tumor’s immune infiltrate. Of note, the tumor also stained positively for PD-L1, a known T-cell inhibitor. The anal SCC also stained positively for CD20 and CD68, revealing the presence of both B cells and monocytes in the infiltrate. SCC: squamous cell carcinoma; HPV: human papilloma virus; PD-L1: programmed death ligand 1.