Melanoma-associated spongiform scleropathy: biochemical changes and possible relation to tumour extension

To investigate biochemical changes of the sclera in eyes with melanoma-associated spongiform scleropathy (MASS), and to analyse possible relationships between these changes and tumour extension.

Sections from 364 eyes, enucleated for choroidal and ciliary body melanoma, were examined for MASS and scleral tumour extension. Biochemical analysis was also performed on eight scleral specimens with MASS and eight specimens (controls) from morphologically normal sclera of the same eyes. The scleral thickness of each specimen was measured. Samples were delipidized, dried and weighed. The weight ratios of collagen-related amino acids were calculated based on quantitation by liquid chromatography. Amounts of glycosaminoglycans (GAGs) were determined by electrophoresis.

Melanoma-associated spongiform scleropathy was seen in 140 eyes (38.5%). Tumour scleral extension was observed in 82 eyes. Of these 82 eyes, 75 (91.5%) had MASS (p<0.05). Biochemically, the majority of the main amino acids of the scleral collagen and total proteins were significantly lower in areas with MASS than in the control specimens. Specific GAGs and total GAGs were found in significantly higher concentrations in areas with MASS than in the control specimens. Scleral thickness was also significantly higher in areas with MASS than in the control specimens.

The reduced content of collagen manifested by decreased amino acids and total proteins indicates collagen degradation in the vicinity of the tumour. The concomitant excessive deposition of GAGs accumulates water and may cause loosening of the already degraded collagen bundles, giving a histopathological picture of MASS. These changes could facilitate tumour cell migration and may explain the high incidence of MASS in eyes with scleral tumour extension.