How cancers are graded
What is cancer grade?
Tumours are graded by the degree of
differentiation and growth rate, often on a scale of 1 to 3, where 3 represents the least differentiated, fastest- dividing tumours. Tumours that more
closely resemble the tissue of origin are graded as well- differentiated (grade 1), while tumours with a more aggressive growth and high mitotic rates are graded as poorly differentiated (grade 3) cancers. The term anaplastic (Greek, ‘to form backwards’) is used to describe tumours that are so poorly differentiated that they
have very few tissue- specific features and often do not stain well to surface markers.
The grade has prognostic significance, with grade 1 tending to have a more favourable prognosis and grade 3 the worst. Formal grading systems exist for a range of cancers but it does remain a subjective assessment, and typically a single cancer can be
heterogeneous such that areas differing significantly in
differentiation and mitotic activity exist side by side, with a risk of sampling error. Therefore for accurate diagnosis and grading, sufficient tissue and microscopic sections must be sampled so that the most malignant areas are found.
Some cancers are so
well differentiated that their malignant cells cannot be distinguished from those of benign tumours or even from normal cells. In such instances, the recognition of abnormal cellular relationships becomes especially important for correct diagnosis.