Mast cell deficiency abates early neoplastic progression. Presence of mast cells (CAE, red staining; A–C), proliferation of keratinocytes (Ki-67, brown staining; D–F), and capillary architecture and densities (CD-31, brown staining; panels G–I) were compared between wild-type littermates (-LM; n = 3; A, D, and G), K14–HPV16 KIT+/KIT+ (n = 8; B, E, and H), and K14–HPV16 KITW/KITWWv (n = 1; C, F, and I) mice. Ear tissue biopsies (5 × 2-mm) were removed from 2-month old littermates, embedded in OCT freezing medium, and sectioned (10 μm). Dashed line indicates epidermal–dermal interface. Arrows point to dilated capillaries subjacent to hyperplastic skin. (f) Hair follicle. Bar, 44.6 μm (A–I).