The most common melanocytic lesion of the conjunctiva is the compound naevus. Other types of naevi that can be found in the conjunctiva are intraepithelial, subepithelial, Spitz and blue naevi. Their histology is similar to melanocytic skin lesions. The naevus mostly arises in the first or second decade as a nodule in the bulbar conjunctiva. A band of melanocytes in the basal layer of the epithelium represents the intraepithelial component. These melanocytes can be melanin-containing, but can also present as clear cells. Melanocytes can also be found in the epithelium of the inclusion cysts, which are almost invariably present. These large, mucin-containing cysts are formed by incarcerated epithelial nests and can give an erroneous clinical impression of growth. The stromal component is formed by nests of mature cells with maturation to smaller cells in the deeper parts of the lesion (Fig. 10.12). Especially at a young age, a considerable variation in cell size can be seen; these active lesions are easily overdiagnosed as malignant melanomas.
Fig. 10.14. Malignant melanoma arising from primary acquired melanosis with atypia: the conjunctival epithelium is ulcerated and the atypical cells spread into the underlying stroma
Primary acquired melanosis (PAM) arises in middle-aged or elderly patients as a stippled, yellow-brown, flat pigmentation of the conjunctiva. Two subgroups of PAM can be recognised: PAM without atypia (benign acquired melanosis) and PAM with atypia. In benign acquired melanosis, there is hyperpigmentation of the basal layer, but there is only a mild increase in melanocytes. The melanocytes can be large, but show little or no cytologic atypia. Although the evolution of PAM is unpredictable, lesions without atypia have a good prognosis. PAM with atypia can disappear spontaneously, can remain stationary or may progress to malignant melanoma. Histologically, there is an increase in atypical melanocytes in the conjunctival epithelium (Fig. 10.13). The atypia can be graded mild to severe. To exclude invasive growth, use of the immunohistochemical marker CD68 can be helpful in identifying melanin-containing cells in the stroma as macrophages.
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Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.