Cancer Grading Based on Cell Differentiation

Understanding the Grading System

The histologic grade of a tumor evaluates how much cancer cells differ from their normal counterparts under microscopic examination, which is distinct from staging, and is based on cell differentiation—the degree to which cancer cells resemble normal, mature cells of the tissue from which they originated 1, 2, 3

Well-differentiated tumors (Grade 1) show cells that closely resemble normal tissue architecture and cellular features, indicating slower growth and better prognosis 1, 2, 3
Moderately differentiated tumors (Grade 2) demonstrate intermediate characteristics between normal and abnormal cellular appearance 1, 2
Poorly differentiated tumors (Grade 3) contain cells that look markedly abnormal compared to normal tissue, with loss of organized structure and increased aggressive behavior 1, 2, 3

The Federation Nationale des Centres de Lutte Contre le Cancer grading system evaluates three parameters to determine malignancy grade: tumor differentiation, necrosis, and mitotic count 1, 2, 3
The sum of these scores determines the final grade (Grade 1: 2-3 points; Grade 2: 4-5 points; Grade 3: 6-8 points) 1, 2, 3

The Gleason score specifically measures the degree of glandular differentiation, adding the two most common histologic patterns (each scored 1-5) to create a final score of 6-10 4
Gleason 6 (3+3): Well-differentiated with organized gland formation 4
Gleason 7: Moderately differentiated with intermediate features 4
Gleason 8-10: Poorly differentiated with minimal to no gland formation 4

The International Society of Urological Pathology (ISUP) grading system for clear-cell and papillary RCC is based on nucleolar size and prominence, which reflects cellular differentiation 8

Grading is a critical prognostic indicator that guides treatment intensity decisions, as poorly differentiated tumors pursue more aggressive courses than well-differentiated counterparts, independent of tumor size or extent of spread 4
Grading provides prognostic information beyond what staging alone offers, and cannot be reliably assigned after preoperative chemotherapy or radiation, as treatment-induced changes alter cellular morphology and obscure the original differentiation pattern 1, 2, 3