Correlation of in vitro 32P counts with histologic features of malignant melanoma of choroid and ciliary body.

The radioactive phosphorus uptake of 30 samples fron nine uveal melanomas was determined by liquid scintillation counting. These in vitro measurements correlated positively with clinical (in vivo) 32P values and with the number of mitotic figures and percentage of epithelioid cells (PEC) within the specimens. Three possible explanations were found for the failure of previous workers to demonstrate a correlation between cell type and clinical 32P. (1) Cell type, using Callender's classification, provides only a crude estimate of the PEC within a tumor; in particular, tumors of mixed cell type can vary widely in epithelioid cell content. (2) The rate of 32P absorption is not su-ficiently sensitive to distinguish spindle cell tumors from mixed cell tumors with a low PEC. (3) Clinical 32P measurements may be affected by extraneous factors that cause large deviations from the expected values.