Figure 2. KS progression: a histological view.

A) Patch stage:

• subtle proliferation of irregular vascular channels between normal stromal collagen
• the extravasation of erythrocytes and hemosiderin into the stroma
• detection of lymphoplasmacytic infiltrate

B) Plaque stage:

• proliferating spindled cells that form interlacing bundles closely approximated with blood-filled vascular spaces
• intracellular hyaline globules within lesional cells (likely representing phagocytosed erythrocytes within lysozomes)
• increased inflammatory infiltrate consisting of lymphocytes, plasma cells, macrophages, and dendritic cells

C) Nodular stage:

• formation of intersecting fascicles and sheets of proliferating spindled cells