California Cancer Reporting System Standards Volume I: Abstracting and Coding Procedures
Pathologic examination determines the grade, or degree of differentiation, of the tumor. For these cancers, the grade is a measurement of how closely the tumor cells resemble the parent tissue (organ of origin). Well-differentiated tumor cells closely resemble the tissue from the organ of origin. Poorly differentiated and undifferentiated tumor cells are disorganized and abnormal looking; they bear little (poorly differentiated) or no (undifferentiated) resemblance to the tissue from the organ of origin. These similarities/differences may be based on pattern (architecture), cytology, nuclear (or nucleolar) features, or a combination of these elements, depending upon the grading system that is used. Some grading systems use only pattern, for example Gleason grading in prostate. Others use only a nuclear grade (usually size, amount of chromatin, degree of irregularity, and mitotic activity). Fuhrman’s grade for kidney is based only on nuclear features. Most systems use a combination of pattern and cytologic and nuclear features; for example Nottingham’s for breast combines numbers for pattern, nuclear size and shape, and mitotic activity. The information from this data item is useful for determining prognosis and treatment.
Pathologists describe the tumor grade using three systems or formats:
Two levels of similarity; also called a two-grade system.
Three levels of similarity; also called a three-grade system (code according to “Coding for solid tumors.”)
Grade I, well.
Grade II, moderately.
Grade III, poorly (undifferentiated carcinoma is usually separated from this system, since “poorly” bears some, albeit little, similarity to the host tissue, while “undifferentiated” has none, e.g. Undifferentiated carcinoma).
Four levels of similarity; also called a four-grade system. The four-grade system describes the tumor as:
Grade I; also called well-differentiated.
Grade II; also called moderately differentiated.
Grade III; also called poorly differentiated.
Grade IV; also called undifferentiated or anaplastic.
Breast and prostate grades may convert differently than other sites. These exceptions are noted in “Coding for Solid Tumors”, see #7-8 in Section V.3.6.2.