Dopa oxidase activity in differential diagnosis of amelanotic melanoma tissue.

The histopathological diagnosis of melanomas with no demonstrable pigment is difficult. Such tumors are to be differentiated from anaplastic carcinomas, especially of the squamous and adeno types, and from sarcomas showing marked anaplasia or spindle cells. In a previous report from this laboratory (1), a colorimetric method for determination of L-3,4-dihydroxyphenylalanine (dopa) oxidase activity in pigmented tissues was described, and it was suggested that a study of the enzymic oxidation of dopa might be of value in human melanomas. I t is the purpose of this paper to present (a) an improved assay procedure and (b) studies of dopa oxidase activity in melanotic and amelanotic types of human melanoma tissue, other malignant tumors, and non-neoplastic tissues.