E6/E7 transgenic mouse phenotype. (a) Gross photograph of an 18 month old E6/E7 transgenic mouse with an enlarged thyroid visible externally. (b and c) Photomicrograph of a thyroid gland from a 6 month old WT mouse at 5x (b) and 20x (c) magnification. (d and e) Photomicrograph of a thyroid gland from a 6 month old transgenic mouse at 5x (d) and 20x (e) magnification. The thyroid follicles are engorged with colloid and are irregular in shape. Also found are solid masses of cells with little or no follicular organization. A papillary carcinoma is evident in (e).