BLEACHING OF MELANIN BEFORE IMAGE CYTOMETRY OF THE DNA CONTENT OF PIGMENTED SKIN TUMORS

OBJECTIVE: To study the effect of bleaching of melanin with KMnO4 on t he results of DNA image cytometry in pigmented skin tumors. STUDY DESI GN: Image cytometry of nuclear DNA content teas performed on sections from 14 melanocytic skin tumors stained with feulgen stain both with a nd without prior bleaching with KMnO4. RESULTS: The nuclear staining i ntensity of Feulgen stain tons lower in the bleached sections, but thi s did not significantly affect the evaluation of ploidy. Heavy pig pig mentation caused some false peaks in the histograms (4 of 28 measureme nts made on unbleached slides). CONCLUSION: Blenching of sections with KMnO4 can be useful when heavy melanin pigmentation would make DNA me asurements impossible or difficult in image analysis cytometry. Bleach ing is not advisable when only lightly pigmented tumors are analyzed i f nuclei obscured by any pigment granules are to be avoided. In large series containing both bleached and nonbleached specimens, statistical analysis of these groups should be separated.