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Human uveal melanoma expresses NG2 immunoreactivity

¹ Centre for Experimental Radiation Oncology, Cancer Care Centre, St George Hospital, Gray Street, Kogarah, NSW, Australia
² Department of Clinical Ophthalmology, Save Sight Institute, University of Sydney, NSW 2006, Australia
³ Anatomical Pathology, Prince of Wales Hospital, Australia
⁴ University of New South Wales, NSW 2052, Australia

Correspondence to:
Correspondence to:
Professor B J Allen, Centre for Experimental Radiation Oncology, Cancer Care Centre, St George Hospital, Kogarah, NSW, 2217, Australia;
b.allen{at}unsw.edu.au

Background/aims: NG2 is the rat homologue of the human melanoma proteoglycan (HMP), also known as the high molecular weight melanoma associated antigen. Most cutaneous melanomas, as well as glioblastomas, chondrosarcomas, and some leukaemias express NG2 immunoreactivity, recognised using monoclonal antibody (mAb) 9.2.27. This antibody has also been used for molecular targeting in targeted therapy for melanoma. The purpose of this study was to evaluate the expression of NG2 immunoreactivity in human uveal melanoma and normal ocular tissue using mAb 9.2.27.

Methods: Enucleated eyes from 26 patients with choroidal or ciliary body melanoma (n=26) were available as paraffin sections, and stained with haematoxylin and eosin to assess for tumour cell type and histopathology. Additional slides were investigated for NG2 immunoreactivity using mAb 9.2.27 and alkaline phosphatase anti-alkaline phosphatase (APAAP) immunostaining. Two independent observers graded immunostaining using a semiquantitative scale from 0 (negative) to 3 (strong).

Results: Immunostaining for mAb 9.2.27 could not be graded in 7/26 cases with dense pigmentation of the tumour. For the remaining cases, grade 2 (moderate) or more immunostaining was seen in 18/19 tumours (95%). The retina, retinal pigment epithelium (RPE), and choroid displayed weak immunostaining (grade 0.5–1.5) in the majority of melanoma affected eyes. Normal retina and choroid (n=5) appeared negative for mAb 9.2.27. Optic nerve axon bundles in both control and melanoma affected eyes displayed moderate immunostaining.

Conclusion: In the present study, the majority of human uveal melanomas expressed NG2 immunoreactivity, as detected using mAb 9.2.27. This antibody may be a suitable candidate for radioimmunotherapy to target ocular melanoma.

Keywords: chondroitin sulphate proteoglycan; monoclonal antibodies; radioimmunotherapy; retina

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