REASSESSMENT OF THE PAS PATTERNS IN UVEAL MELANOMA

Background-Previous work has highlighted the prognostic importance of patterns of periodic acid Schiff (PAS) staining (the Folberg patterns) in uveal melanoma. These patterns have been ascribed to blood vessels but the patterns are different from those seen with other staining te chniques for blood vessels. It has recently been shown that microvesse l density is the dominant prognostic factor in uveal melanoma. This st udy reinvestigates the nature and significance of the PAS patterns. Me thods-The PAS patterns were compared with the patterns seen with conve ntional connective tissue stains and with the patterns seen in section s stained for the presence of blood vessels (by immunohistochemistry f or factor VIII related antigen). The PAS patterns were determined on a panel of 117 cases of uveal melanoma. The prognostic significance of each of these patterns was determined and, as more than one pattern ca n exist in a tumour, principal components analysis was performed to de termine the number of underlying factors. Results-Comparison of the PA S patterns with other stains demonstrates that they are based on conne ctive tissue including fibrovascular tissue. Five of the nine PAS patt erns carried prognostic significance on univariate analysis. Principal components analysis suggested that these patterns represented three u nderlying factors, which were tentatively identified as representing d isordered growth (factor 1), emergence of rapidly growing subclones (f actor 2), and section orientation (factor 3). Conclusions-The PAS patt erns are based on fibrovascular tissue and can be ascribed to three un derlying factors. The first two of these factors carried prognostic si gnificance and the first (disordered growth) retained independent prog nostic significance in a multivariate Cox model which included microve ssel density and tumour size.