Local conjunctival metastases from primary conjunctival melanoma: clinico-pathological correlation and implications

A retrospective service evaluation identified seven patients who developed local conjunctival metastases (LCMs) of the conjunctiva after a primary diagnosis of conjunctival invasive melanoma. The study was conducted to identify the clinico-pathological characteristics and implications of these LCMs.

Seven patients with primary conjunctival melanoma seen by the ocular oncology service were identified as having also developed LCMs. The clinical history, histopathology, tumour biology, prognostic and staging implications of LCMs were evaluated.

A total of 15 primary conjunctival melanomas and 19 LCMs were identified. The LCM developed 8-102 months after the first primary melanoma and, in three patients, non-conjunctival metastases developed 8-37 months after the first LCM. The LCMs showed some distinct histopathological features: they were well defined, were separated from the overlying epithelium by a Grenz zone, and were often multiple and associated with vessels and sometimes lymphocytic aggregates. Some appeared within the confines of the vascular drainage territory of the primary melanoma; others did not confine themselves to this distribution.

LCMs are local metastases of primary conjunctival melanoma that probably develop by dissemination through the local vessels and then becoming extavascular. Their accurate histopathological recognition is important, as it indicates a higher disease stage-indicating 'N' status within the TNM classification and may be a proxy indicator of the presence of non-conjunctival metastases, thus necessitating high-resolution radiological imaging modalities or sentinel node biopsy. LCMs may represent an under-recognised lesion and may have been mistaken for primary 'nodular' conjunctival melanomas in the past.