Background Deep penetrating nevus (DPN) is not a widely recognised lesion on the conjunctiva and only a few cases consistent with combined DPN have been reported.

Methods A review of all excised and histopathologically diagnosed conjunctival melanocytic lesions between 2003 and 2018 was performed in order to identify melanocytic nevi morphologically consistent with DPN.

Results Thirty-four DPN were identified among 361 histopathologically examined conjunctival nevi (9.4%), including 33 (97%) combined with a common nevus and 1 (3%) pure DPN. The patients’ age ranged from 7 to 51 years (median, 22 years). Clinically, 21 of 29 (72%) lesions with available data were darkly pigmented, and an increase in size and/or pigmentation was noted in 13 of 18 (72%) lesions with known history. All 24 lesions in which an immunohistochemical analysis was possible were diffusely positive for BRAFV600E (in DPN and common nevus components) and showed a diffuse nuclear positivity for beta catenin and cyclin D1 in the DPN component. None of the 21 lesions with available follow-up data recurred during a follow-up period from 0.3 to 16.3 years (median, 7.5 years).

Conclusions DPN of the conjunctiva is a relatively common lesion and usually presents as a combined nevus. Genetically, DPN of the conjunctiva are characterised by a combination of BRAFV600E mutation and activation of the beta catenin pathway. Recognition of DPN of the conjunctiva is important in order not to overdiagnose it as a melanoma, and to explain its potential atypical clinical features. DPN of the conjunctiva seems to be a benign lesion.