A Case of Adenocarcinoma of the Retinal Pigment Epithelium: An Immunohistochemical and Electron Microscopic Study

Abstract

Purpose: Retinal pigment epithelium (RPE) adenocarcinoma is a very rare malignant intraocular tumor. Herein we describe the histopathological features of RPE adenocarcinoma. Case: A 36-year-old male was referred to our clinic because of floaters in his left eye. The initial diagnosis was malignant melanoma of the choroid. We resected the tumor and studied it histopathologically. The tumor tissue was investigated by light microscopy including immunohistochemistry using antibodies against S-100, HMB-45, EMA, and AE-1. Electron microscopic examination was also performed. Results: The tumor arose from the RPE and contained intracytoplasmic vacuoles and abundant melanin pigment. There were no nevoid cells in the choroid. A small part of the tumor cells showed tubular or lobular proliferation and choroidal invasion. Immunohistochemistry revealed positive staining in tumor cells with 4 antibodies. Tight cellular junctions specific to the RPE were confirmed by electron microscopy. The final diagnosis was RPE adenocarcinoma. Conclusions: Most pigmented intraocular tumors are nevus and malignant melanomas of the choroid. It is easy to misdiagnose a RPE adenocarcinoma as a malignant melanoma of the choroid. An exact differential diagnosis should be determined by immunohistopathological and electron microscopic examination.

Retinal Pigment Epithelium Adenoma and Adenocarcinoma: A Review

“…A particularly important feature of RPE adenocarcinoma is the occasional presence of a dilated retinal feeder vessel [12]. Shields et al [3] found dilated retinal vessels in 8 of 13 RPE tumours in their study, which were accentuated on fluorescein angiography.…”

“…In the middle of the spectrum, there are lesions for which no clear distinction between hyperplasia and true neoplasms can be made, either clinically or histologically [11]. It has been acknowledged that RPE tumours can arise from reactive hyperplasia and metaplasia following trauma, inflammation, or degenerative processes that involve the choroid or retina [12]. They have been reported to arise from congenital hypertrophy of the retinal pigment epithelium (CHRPE) as well [13][14][15][16][17][18].…”

“…Magnetic Resonance Imaging RPE tumours are reported to be hyperintense in T1 and hypointense in T2 [12,37]. Unfortunately, MRI may not differentiate RPE tumours from other tumours such as malignant melanoma or choroidal haemangioma since the imaging properties are similar [38].…”

“…The most common presenting symptoms are a gradual diminution of vision [2], followed by floaters [12, 20, 21]. Small peripheral tumours may be asymptomatic and detected at a routine eye check-up.…”

“…Electron microscopy shows tight junctions between the tumour cells and apical microvilli with mature and large melanosomes [12, 32, 42]. Font et al [42] described 2 types of tumour cells seen on electron microscopy, namely, light and dark cells.…”