What does Ki-67 mean on a pathology report

Understanding Ki-67 on Your Pathology Report

Ki-67 is a protein that measures how fast cancer cells are dividing and growing. Think of it as a "proliferation index" — essentially a snapshot of how active your cancer cells are at the cellular level.

How It Works

When pathologists examine your cancer tissue under a microscope, they use special stains to identify which cells are actively dividing. Ki-67 is a marker that appears in cells that are in the process of reproducing. The pathologist counts what percentage of cancer cells show this marker.

What the Percentage Means

Ki-67 is reported as a percentage (for example, "Ki-67: 20%"):

• Low Ki-67 (typically <10-15%): Cancer cells are dividing slowly — generally associated with slower-growing cancers
• Intermediate Ki-67 (15-30%): Moderate growth rate
• High Ki-67 (>30%): Cancer cells are dividing rapidly — suggests more aggressive behavior

Why Doctors Care About This

According to NCCN Guidelines and ASCO recommendations, Ki-67 helps oncologists:

• Assess how aggressive your cancer is
• Predict how the cancer might behave
• Help guide treatment decisions (particularly in breast cancer, where it influences hormone therapy vs. chemotherapy choices)
• Estimate prognosis alongside other factors

Important Context

Ki-67 is one piece of information among many. Your doctor considers it alongside:

• Tumor grade and stage
• Hormone receptor status (ER/PR)
• HER2 status
• Other biomarkers specific to your cancer type

Questions to Ask Your Doctor

1. What is my specific Ki-67 percentage, and what does that mean for my cancer?
2. How does my Ki-67 result influence your treatment recommendations?
3. Are there other markers you're considering alongside Ki-67 in my case?

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.