BRAF, NRAS, and GNAQ Mutations in Conjunctival Melanocytic Nevi

Abstract

Purpose: To evaluate BRAF, NRAS, and GNAQ mutations in surgical specimens of common and blue conjunctival melanocytic nevi.

Methods: Surgical specimens from 25 conjunctival melanocytic nevi (23 common and 2 blue) of 25 patients were evaluated. All common nevi were analyzed immunohistochemically for the expression of BRAF V600E or NRAS Q61R. One lesion with negative immunoreactivity and for all blue nevi, a hybridization capture-based next-generation sequencing method was employed for mutation analysis. For common nevi, genetic features were compared with clinical and histopathologic findings. Continuous variables (age at excision and largest basal diameter) were compared with a Students's t-test and all categoric variables were compared with Fisher's Exact Test.

Results: Of common melanocytic nevi, 9 (39.1%) were immunoreactive for NRASQ61R and 13 (56.5%) were immunoreactive for BRAFV600E. One common nevus, which was immunonegative for both BRAFV600E and NRASQ61R was found to harbor an NRASQ61K mutation by sequence analysis. Patients with NRAS-mutated nevi were more likely to report occurrence of the lesion prior to 18-years old and more likely to have intrinsic cysts. The mean largest basal diameter was 6.0 and 3.5 mm for NRAS- and BRAF-immunoreactive lesions, respectively (P = 0.003). GNAQ mutations were identified in each of the two blue nevi of this study.

Conclusions: These findings document that common conjunctival melanocytic nevi have mutually exclusive mutations in BRAF and NRAS. The two conjunctival blue nevi harbored GNAQ mutations. This suggests the driver mutations of conjunctival nevi are similar to those of nevi of the skin. At the molecular level, conjunctival nevi appear more like cutaneous nevi than choroidal nevi.

Figure 1

Conjunctival nevus occurring in childhood. (A) Clinical photo demonstrating intrinsic cysts, diameter of 3.5 mm and amelanotic appearance. (B) Histopathology of a compound melanocytic nevus with epithelial cysts and evidence of maturation (×10, hematoxylin and eosin). (C) The junctional and subepithelial melanocytes are immunohistochemically positive for NRASQ61R (×10, peroxidase antiperoxidase).

Figure 2

Conjunctival nevus occurring in adulthood. (A) Clinical photo demonstrating absence of intrinsic cysts, diameter of 1.5 mm and a deeply melanotic appearance. (B) Histopathology of a melanocytic nevus (×10, hematoxylin and eosin). (C) The melanocytes are immunoreactive for BRAFV600E (×10, peroxidase antiperoxidase).

Figure 3

Conjunctival blue nevus. (A) Clinical photo demonstrating heterochromic bulbar lesion with areas of deep melanosis. (B) Histopathology of a blue nevus characterized by pigmented slender fusiform and dendritic melanocytes in the subepithelial stroma (×10, hematoxylin and eosin).