Primary acquired melanosis (PAM)/conjunctival melanocytic intraepithelial neoplasia (C‑MIN). A, Mild PAM, involving 1 clock-hour of conjunctiva; unlikely to harbor atypia and may be observed. B, Histology of PAM (C-MIN) without atypia. H&E stain (top) shows melanocytic proliferation, confined to the basal layer of the epithelium (between the 2 arrows), with no cellular atypia. Melan‑A (MART‑1) immunohistochemical stain (bottom) highlights the increased number of small dendritic melanocytes, arranged linearly in the region of the basal epithelium (arrows). C, Extensive PAM, involving much of the ocular surface, including the caruncle, palpebral conjunctiva, and eyelid margin; likely harbors atypia and warrants biopsy. D, Histology of PAM (C-MIN) with mild to moderate atypia, mostly in the basal epithelial layer (arrowheads); the melanocytes are small, without prominent nucleoli. Some melanocytes are seen in the superficial epithelium, singly and in nests (arrows). There is a moderate risk of transformation to melanoma. E, Histology of PAM with severe atypia (melanoma in situ). The minimally pigmented melanocytic proliferation (arrows) involves most of the epithelial thickness. Some atypical melanocytes have epithelioid morphology. F, PAM with severe atypia (different patient). Higher magnification shows epithelioid melanocytes (arrows) within the epithelium. These latter two lesions are at significant risk for progression to melanoma.