Ki-67 index is a lab measurement that estimates how many tumor cells are actively dividing. It is reported as a percentage based on staining of a biopsy or surgical tissue sample. Clinicians use it most often in cancer pathology reports to describe tumor “proliferation” (growth activity). It is commonly discussed in solid tumors and some blood cancers, alongside tumor grade and stage.

WHO grading is a standardized way to describe how a tumor looks under the microscope and how aggressive it may behave. It is published within World Health Organization (WHO) tumor classification systems used by pathology and oncology teams. WHO grading is commonly reported after a biopsy or surgery when a pathologist examines tumor tissue. It helps clinicians communicate risk and plan care, alongside staging and other test results.

Fuhrman grade is a way pathologists describe how aggressive certain kidney cancers appear under a microscope. It is based on how the tumor cell nuclei look, including size, shape, and how prominent nucleoli are. It is most commonly discussed in renal cell carcinoma (RCC), especially clear cell RCC. It appears on a pathology report after a biopsy or surgery removes tumor tissue.

Bloom-Richardson grade is a pathology grading system that describes how aggressive an invasive breast cancer appears under the microscope. It summarizes several microscopic features into a single grade that helps communicate tumor behavior. It is most commonly reported for invasive breast carcinoma in biopsy or surgery pathology reports. It is sometimes referred to as the Nottingham (Elston–Ellis) histologic grade in many clinical settings.

Elston-Ellis grade is a pathology grading system used most commonly for invasive breast cancer. It describes how abnormal the cancer cells and tissue architecture look under a microscope. The grade helps summarize tumor “differentiation,” meaning how much the tumor resembles normal breast tissue. Clinicians use it alongside stage and biomarker results to understand prognosis and plan care.

Nottingham grade is a pathology-based way to describe how “aggressive-looking” certain breast cancers appear under the microscope. It is most commonly used for invasive breast carcinoma on biopsy or surgery samples. The grade summarizes three microscopic features into a single score that helps estimate tumor behavior. It is different from cancer stage, which describes how far cancer has spread.

Clark level is a pathology term that describes how deeply a melanoma has grown into the layers of the skin. It is determined by examining a skin biopsy under a microscope. It is most commonly discussed in cutaneous (skin) melanoma reports and older staging systems. Today it is often considered alongside, or secondary to, other measures such as Breslow thickness.

Breslow depth is a pathology measurement of how deep a melanoma extends into the skin. It is reported in millimeters and is based on what a pathologist sees under a microscope. It is most commonly used for cutaneous (skin) melanoma after a biopsy or excision. It helps clinicians estimate risk and plan next steps such as surgery and lymph node evaluation.

ISUP grade group is a pathology grading system most commonly used for prostate cancer. It summarizes how aggressive a prostate tumor looks under the microscope. It is reported from prostate biopsy or prostate surgery tissue. It helps clinicians communicate risk and plan care in a consistent way.

Gleason score is a pathology grading system used to describe how prostate cancer looks under a microscope. It summarizes how closely the cancer tissue resembles normal prostate tissue. It is most commonly reported after a prostate biopsy or after surgery to remove the prostate. It helps clinicians communicate cancer aggressiveness in a standardized way.