THE METACHROMATIC STAINING REACTION Lison's (1935) classical studies on the metachromatic staining reaction led him to conclude that the capacity to stain metachromatically was the exclusive property of sulphuric acid esters of high molecular weight. He stipulated that the reaction was specific only if carried out under conditions unfavourable to the development of the metachromatic colour, and suggested that this is most easily AND G. M. WINDRUM

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Introduction:Keratoacanthoma (KA) and invasive squamous cell carcinoma (SCC) are keratinocytic tumors displaying vascular features, imaged using dermatoscopy.Objective:Compare the dermatoscopy vascular features of KA to SCC.Methods:This prospective study examined consecutive cases of 100 KA and 410 invasive SCC in a single private practice in Sydney, Australia. Vascular features were recorded in vivo direct from patients using a non-polarized Delta 20 Heine dermatoscope. These vascular features were: linear, branching, serpentine, hairpin, glomerular and dot vessels, the presence or absence of large diameter tumor vessels, vessel presence in central verses peripheral tumor areas and tumor pink areas in different proportions. Following full excision, all cases were submitted for histopathologic diagnosis.Results:Branching vessels were the only vessel morphology that varied, with a significant incidence in KA (25.0%), compared to SCC (10.7%), P < 0.01. Large vessels were identified in 20.0% of KA, compared to 12.4% in SCC, P = 0.05. No vessels were observed in the central tumor areas in 43.4 % of KA compared to 58.0% of SCC, P = 0.01. Other data comparing the central versus peripheral tumor areas for vessels present did not reveal any distinctive associations. There were no significant differences between KA and SCC when reviewing the selected proportions of pink within the tumor.Limitations:The vascular features may be confounded by tumor depth in KA. Polarized dermatoscopy may not produce the same findings.Conclusion:This study found branching vessels to have a higher incidence in KA compared to invasive SCC. Although not statistically significant, large diameter vessels were also more frequent in KA. Proportions of pink within the tumor or central verses peripheral tumor vessel distribution were not useful diagnostic features separating KA from SCC using dermatoscopy.

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