Several international standards define how tumors are classified histologically. These resources are often available in digital or PDF formats for professional use:

: Manages the WHO Blue Books series , including the latest 5th and 6th editions.

Histopathological classification is the cornerstone of modern oncology, providing the precise diagnosis necessary to guide treatment and predict patient outcomes. By examining tissue samples at a microscopic level, pathologists categorize tumors based on their cell of origin and degree of abnormality, directly influencing clinical decisions. Key Reference Frameworks

: Pathologists assign a grade (typically 1 to 4) to describe how much the tumor cells resemble normal cells. Grade 1 indicates well-differentiated (low-grade) cells, while Grade 4 indicates undifferentiated (high-grade) cells.