Immunohistochemical analysis of benign and malignant melanocytic lesions of the conjunctiva using double-staining

To implement a double-staining technique to identify the most sensitive and specific combinations of melanoma antigen recognized by T cells (Melan-A), microphthalmia-associated transcription factor (MITF), human melanoma black 45 (HMB45), and Ki67 aiming to assist in the diagnosis of atypical melanocytic conjunctival lesions that are more prone to malignant progression.

Eight specimens of conjunctival melanoma and of primary acquired melanosis with moderate to severe atypia were double-immunostained with a combination of a cytoplasmic marker (anti-Melan-A or anti-HMB45), and a nuclear marker (anti-MITF or anti-Ki67). Eight specimens of normal conjunctiva and of conjunctival nevi served as controls. The specimens were processed using 3,3-diaminobenzidine substrate for nuclear stains and the fast-red substrate for cytoplasmic stains. Each slide was analyzed by light microscopy and provided a percent scale and a 0 to 4+ score for each nuclear and cytoplasmic component.

Melan-A and MITF were strongly positive markers for all melanocytic cells, whereas Ki67 and HMB45 provided a variable response for identifying potentially proliferative or aggressive cells. HMB45 and MITF proved to be the best combination for differentiating between atypical and benign lesions on a percent scale and a 0 to 4+ scale (p = 0.0004), with the 3 other combinations providing mainly confirmatory diagnostic information (p < 0.05).

Our study used an immunohistochemical double-staining approach to differentiate between atypical and benign melanocytic lesions of the conjunctiva. Our findings should aid in a more complete immunohistopathological diagnosis of conjunctival melanocytic lesions, particularly in diagnostically difficult cases.