Understanding a tumor’s specific characteristics is an important part of developing an effective breast cancer treatment plan. Various diagnostic markers provide insights into how a tumor behaves. These markers help medical professionals categorize breast cancers and predict their potential response to different therapies.
Understanding Ki-67
Ki-67 is a protein found inside the nucleus of human cells. Its presence indicates cellular proliferation, the process of cell division or growth. Ki-67 is present during all active phases of the cell cycle (G1, S, G2, and mitosis) but is absent when cells are in a resting phase (G0).
Cancer cells often divide at an uncontrolled and accelerated rate compared to healthy cells. By measuring the amount of Ki-67 in a tumor, medical professionals gain insight into how quickly the cancer cells are multiplying.
Measuring Ki-67 Levels
Ki-67 levels in breast cancer are determined from a tissue sample obtained through a biopsy or during surgery. Pathologists use immunohistochemistry (IHC). This method involves staining the tissue sample with a special antibody that attaches to the Ki-67 protein within the cells.
After staining, a pathologist examines the tissue under a microscope. They count the percentage of cancer cells that show positive Ki-67 staining, which indicates active division. This count results in the “Ki-67 score” or “Ki-67 index,” expressed as a percentage. Only nuclear staining is considered positive; the stain’s intensity does not matter.
Interpreting Ki-67 Scores
The Ki-67 score provides information about the tumor’s growth rate. A low Ki-67 score indicates a slower-growing tumor, while a high score suggests more rapid cell division. For instance, a Ki-67 index below 10-14% points to a slower-growing tumor. These tumors are less likely to spread quickly.
Conversely, a high Ki-67 score, above 20-30%, suggests a tumor that may be more aggressive. Some studies and guidelines consider a score over 20% to be high, while others might use 14% or even 30% as a threshold. This variability in cutoffs means that interpretation should always be done by a medical professional who considers the patient’s specific context.
Ki-67 and Treatment Planning
Ki-67 results contribute to treatment planning alongside other tumor characteristics, such as hormone receptor status (ER/PR), HER2 status, and tumor grade. A high Ki-67 score might indicate that a tumor is more likely to respond well to chemotherapy, as chemotherapy targets rapidly dividing cells. For example, in some cases, a Ki-67 index of 20% or higher might lead to a recommendation for chemotherapy.
For tumors with a low Ki-67 score, particularly those that are hormone receptor-positive and HER2-negative, endocrine therapy alone might be considered sufficient. This is because slower-growing tumors may respond effectively to less aggressive approaches. Ki-67 is one piece of a larger diagnostic puzzle, and treatment decisions are made by integrating all available information about the tumor’s biology and the patient’s overall health.
Considerations for Ki-67 Testing
While Ki-67 is a useful marker, its testing can involve some variability. Results can differ between laboratories or even within different sections of the same tumor. This is because there is not yet a single, universally standardized method for assessing Ki-67, which can lead to inconsistencies in scoring.
Despite these challenges, efforts are ongoing to standardize Ki-67 testing and improve its consistency and predictive power. It is important to remember that Ki-67 is not a standalone predictor of a patient’s outcome. Its interpretation should always be performed by a medical professional who considers the patient’s complete clinical picture.