Diagnostic code book first published in 1976 for classifying morphology of neoplasms. Of the five digits, the first four identify the histology of the neoplasm and the fifth identifies the neoplasm as either benign, uncertain, carcinoma in situ, primary malignant, secondary malignant, or unknown whether primary or secondary. Cancer registry centers in hospitals and ambulatory care centers use this code system for classification of tumors. Also known as morphology of neoplasms .