A “CK5/6 positive” result on a medical report indicates the presence of Cytokeratin 5 and/or Cytokeratin 6, which are structural proteins. This finding typically arises during diagnostic testing when pathologists analyze tissue samples. This protein marker provides information that helps healthcare professionals classify cells and characterize diseases.
Understanding CK5/6
CK5/6 refers to Cytokeratin 5 and Cytokeratin 6, intermediate filament proteins that are part of the cytoskeleton. This network helps cells maintain their shape and internal organization. Cytokeratins are primarily found in epithelial cells, which line organs and glands. Their function is to provide structural integrity and mechanical stability. CK5 and CK6 are typically expressed in the basal cells of squamous epithelium, such as skin, and certain glandular epithelia.
Testing for CK5/6
Detection of CK5/6 in tissue samples is performed using immunohistochemistry (IHC). During IHC, a tissue sample, often obtained through a biopsy, is treated with specific antibodies designed to bind to the CK5/6 proteins. A secondary antibody, linked to an enzyme that produces a color change, is then added.
If CK5/6 proteins are present, a visible color reaction occurs under a microscope, indicating a “positive” result. A “CK5/6 positive” result signifies the protein was detected above a certain threshold. Conversely, a “negative” result means the protein was not detected or was below the detectable limit. This staining helps pathologists identify cell origin and type. The process typically takes 1-3 days.
CK5/6 in Cancer Diagnosis
CK5/6 positivity serves as a biomarker in diagnostic pathology, classifying tumor types for accurate diagnosis and treatment planning. It is commonly observed in squamous cell carcinomas, cancers arising from squamous epithelial cells found in the lung, head and neck, esophagus, and cervix. For instance, in lung cancer, CK5/6 distinguishes squamous cell carcinoma from adenocarcinoma.
The marker is also relevant in diagnosing mesothelioma, a cancer linked to asbestos exposure. CK5/6 positivity helps differentiate epithelioid mesothelioma from other cancers, like lung adenocarcinoma, where it is typically absent. While effective for epithelioid mesothelioma, its reliability is lower for sarcomatoid and biphasic subtypes, necessitating complementary tests.
In breast cancer, CK5/6 positivity can indicate a “basal-like” molecular subtype, often associated with triple-negative breast cancer, which may have different treatment implications. Some studies suggest CK5 alone may be more sensitive in identifying basal-like breast carcinomas.
Interpreting Your CK5/6 Results
A CK5/6 positive result is rarely interpreted in isolation. It is one piece of a larger diagnostic puzzle that pathologists and clinicians assemble. Healthcare providers consider this result alongside other diagnostic information, including additional immunohistochemical markers, imaging scans, tissue biopsy findings, and the patient’s clinical history.
For example, in mesothelioma diagnosis, CK5/6 is often evaluated with other markers like calretinin or WT1 to enhance diagnostic accuracy. The significance of a CK5/6 positive result varies by tissue and clinical context.
Discuss your CK5/6 results with a qualified healthcare professional, such as an oncologist or pathologist. They can explain what the result means for your situation, how it contributes to your diagnosis, and potential next steps.