Abstract: A diagnostic process is disclosed for detecting very early or developed stages of malignancy of tissue beneath a predetermined portion of the skin of a human patient. A sample of body secretion is obtained from the outer surface of the skin and is tested for presence of markedly decreased free, naturally occurring amino acids. The test has approximately the same order of sensitivity as a standard ninhydrin test. The diagnostic process of the invention is particularly adapted for mass screening of human females for early stages of breast cancer.