Conjunctival amelanotic malignant melanoma arising in primary acquired melanosis sine pigmento.

Background: The authors describe an amelanotic malignant melanoma of the conjunctiva in association with primary acquired melanosis (PAM) sine pigmento, and highlight the clinical and pathologic features of this rare entity.
Methods: Histopathologic and immunohistochemical studies were performed on a conjunctival tumor in a 54-year-old white woman.
Study Design: Case report.
Results: Histopathologic examination revealed an invasive amelanotic melanoma of the conjunctiva, with anterior orbital extension arising from intraepithelial dysplastic melanocytes that lacked melanin pigment (PAM sine pigmento). Both the malignant melanoma cells and the intraepithelial dysplastic melanocytes in the areas of PAM exhibited S-100 and HMB-45 positivity. The patient underwent an orbital exenteration that disclosed tumor within the anterior orbit inferiorly.
Conclusions: Amelanotic invasive malignant melanoma can arise in association with PAM sine pigmento, as seen in our patient who had orbital invasion necessitating exenteration. This aggressive form of conjunctival melanoma is often associated with a poor prognosis and risk of metastatic disease. Absence of conjunctival pigmentation in PAM sine pigmento prevents early clinical detection of this variant of PAM. This lack of pigmentation also makes clinical diagnosis virtually impossible, and diagnosis can only be established histopathologically. Awareness of this nonpigmented variety of PAM is crucial for early recognition and appropriate management of the associated melanoma.