An increase in the assay value of CA 15.3 is frequently found in certain types of breast cancer,as in certain lung cancers, but also incertain non -cancerous pathologies. The CA 15.3 assay level decreases after therapy and increase in cases of relapse, residualdisease & metastasis. The CA 15.3 test is used as an additional test for the prognosis and monitoring of therapy for patients withdiagnosed malignant tumours. A decrease in the CA 15.3 assay levels can indicate a positive response to the CA 15.3 assay valueoften reflects evolution of the tumour and a poor response to therapy.