Ki‑67 tests detect a nuclear protein present only in actively dividing cells, so they measure the proportion of tumor cells undergoing cell cycle phases (G1, S, G2, M) versus resting (G0). Results are reported as a Ki‑67 index—the percentage of tumor cell nuclei that stain positive by immunohistochemistry—serving as a marker of tumor cell proliferation.

Clinically, a higher Ki‑67 index generally indicates faster tumor growth and a worse prognosis and can help guide treatment choices (for example, favoring chemotherapy over less aggressive therapy in some cancers). However, interpretation is affected by assay methods, scoring variability and inconsistent cutoff values, so Ki‑67 is used alongside other pathology and clinical information rather than as a standalone decision tool.

Ki‑67 is measured on tumor tissue, not from blood or saliva; the sample is usually obtained during a core‑needle biopsy, incisional or excisional biopsy, or surgical removal of the tumor. The tissue is fixed (commonly in formalin), embedded in paraffin, thinly sectioned and processed in the pathology lab where an immunohistochemical stain for Ki‑67 is applied and the percentage of tumor cell nuclei that stain positive (the Ki‑67 labeling index) is reported.

Proper collection, fixation and laboratory processing are important for accurate results, and the Ki‑67 percentage is interpreted alongside other clinical and pathology information by your healthcare team; this summary is informational and not a clinical diagnosis.

Ki‑67 measures how many cells in a tumor are actively dividing and is reported as the percent of tumor cells that stain positive. A higher Ki‑67 percentage generally indicates a more rapidly growing, often higher‑grade tumor and is associated with a greater likelihood of aggressive behavior and a less favorable prognosis in many cancers; a low Ki‑67 suggests slower growth and usually a more indolent course.

Ki‑67 is one piece of prognostic information — it is not a definitive test of “cancer risk” on its own, not a diagnostic screen, and its clinical meaning depends on the cancer type, stage, other biomarkers (e.g., hormone receptors, HER2 in breast cancer), and treatment context. Lab methods and cutoffs vary, so your exact percentage should be interpreted by your oncology team who will combine it with pathology, imaging and clinical factors to inform prognosis and treatment decisions.

Ki‑67 measures the proportion of tumor cells in active phases of the cell cycle and therefore provides an estimate of how rapidly a tumor is proliferating. It can be a useful prognostic indicator in several cancers (for example, helping to distinguish more from less aggressive breast cancer subtypes) and is commonly used alongside other clinical and pathological features to inform prognosis and treatment decisions.

However, Ki‑67 is not perfectly reliable on its own: results can vary with tissue handling, the antibody and staining protocol used, whether scoring focuses on “hotspots” or overall tumor area, and between observers or laboratories. There are no universally accepted cutoffs for many tumor types, so reproducibility and clinical interpretation improve when labs follow standardized protocols, report methodology and thresholds, and where possible use digital image analysis or consensus scoring. Clinicians therefore interpret Ki‑67 together with other markers and clinical factors rather than as a standalone determinant.

Ki‑67 is usually measured on the tumor tissue (immunohistochemistry) at the time of diagnosis and is not a routine serial blood marker; repeat testing is generally only done when there is a new biopsy (for example at recurrence or progression), when assessing response to neoadjuvant therapy (pre‑ and post‑treatment), or when a result would directly influence treatment decisions.

Because scoring methods and cutoffs vary by lab and tumor type, there is no fixed interval for retesting—frequency should be individualized and guided by your oncologist or pathologist, who will order repeat Ki‑67 only if it will affect management.

No — Ki-67 test results are not diagnostic. They indicate patterns of cellular imbalance or proliferative resilience (how many cells are actively dividing), not a medical diagnosis in themselves.

Ki-67 should be interpreted by a qualified clinician together with symptoms, medical history, imaging, and other laboratory or biomarker data to guide diagnosis and treatment decisions.

Ki‑67 is a tissue-based marker that reflects how quickly tumor cells are dividing; you don’t “improve” the number directly outside of treating the cancer. Reductions in Ki‑67 are achieved by effective cancer therapy (for example, surgery/radiation to remove the tumor and systemic treatments—chemotherapy, endocrine therapy for hormone‑receptor positive disease, or targeted agents when appropriate). In some settings clinicians use neoadjuvant therapy and repeat biopsies to document a fall in Ki‑67 as a measure of response; enrollment in clinical trials may also provide options when standard therapies are limited.

Talk with your oncologist about what your Ki‑67 result means for prognosis and treatment choices in your specific cancer type, stage, and receptor/biomarker profile. Maintain general health measures (stop smoking, follow a balanced diet, exercise, manage comorbidities) to support treatment tolerance, but rely on evidence‑based cancer treatments to change tumor proliferation—do not delay recommended therapy while seeking to alter Ki‑67 by non‑medical means.