A “CK7 Positive” tumor result comes from immunohistochemistry (IHC), a specialized pathology test. This finding means the tumor cells contain the protein marker Cytokeratin 7. Pathologists use this result to identify the tissue type from which a tumor originated, particularly when cancer has spread from its primary site. Understanding this helps doctors narrow down the primary source of the malignancy, which is necessary for determining the appropriate treatment plan.
Understanding Cytokeratin 7
Cytokeratin 7 (CK7) is a protein belonging to the intermediate filament family, which forms the cell’s internal structural network, or cytoskeleton. These filaments provide mechanical strength and maintain cell shape and integrity. CK7 is classified as a Type II keratin and forms a complex with a Type I keratin.
CK7 is restricted to epithelial cells, which line the surfaces of organs and glands, including the lungs, ovaries, and breast ducts. Different epithelia express unique combinations of cytokeratin proteins, creating a biochemical signature for each tissue. A CK7 positive result means the tumor cells retained this expression pattern from their cell of origin.
IHC is the method used to detect this protein, allowing pathologists to visualize specific proteins within a tissue sample. Specialized antibodies are applied to a tissue slide, designed to bind only to the target protein, CK7. The binding of the antibody is then made visible, usually by causing a color change under the microscope, confirming the protein’s presence and location in the tumor cells.
The Diagnostic Purpose of CK7 Testing
The CK7 test is most frequently ordered for patients with a metastatic tumor where the original site is unknown, a situation called Cancer of Unknown Primary (CUP). Since treatment is specific to the original tumor type, identifying the primary site is necessary for guiding therapy. The CK7 result provides a clue in solving this diagnostic puzzle.
Tumor cells generally maintain the cytokeratin profile of the normal epithelial cells from which they arose. A CK7 positive result suggests the tumor originated from an organ that expresses this protein, such as the lung, breast, or ovary. Conversely, a CK7 negative result rules out these origins and directs investigation toward organs that do not express CK7, like the colon or prostate.
This testing provides a chemical fingerprint of the tumor’s ancestry, helping to avoid broad, non-specific treatments. By narrowing the list of potential primary sites, the CK7 result allows doctors to focus on targeted therapies or fewer diagnostic tests.
Cancer Types Most Often CK7 Positive
A positive CK7 result is associated with several common tumor types arising from glandular and ductal epithelia. The CK7 result alone is not a definitive diagnosis but indicates a likely tissue of origin. The most frequent primary tumors exhibiting a CK7 positive profile are adenocarcinomas of the lung, breast, and female reproductive organs.
Lung Adenocarcinoma
Lung Adenocarcinoma is a common cancer that is CK7 positive in a large majority of cases. This finding helps distinguish primary lung cancer from a metastasis that spread to the lung. CK7 positivity in lung cancer is often coupled with the marker TTF-1 to confirm pulmonary origin.
Ovarian Cancer
Ovarian Cancer, especially serous and endometrioid subtypes, is highly likely to be CK7 positive. When a tumor is found in the abdomen or pelvis, a strong CK7 positive stain helps confirm an ovarian or related gynecological origin. This marker helps differentiate ovarian tumors from gastrointestinal tumors, which have a different cytokeratin pattern.
Breast Cancer
Breast Cancer, specifically ductal adenocarcinomas, consistently exhibits CK7 positive status in nearly all cases. If a breast cancer metastasis is found before the primary tumor is detected, the CK7 positive result points toward a mammary origin. This association leads to further testing for hormone receptors like Estrogen Receptor (ER) and Progesterone Receptor (PR) to finalize the diagnosis.
Endometrial Cancer
Endometrial Cancer, arising from the lining of the uterus, is frequently CK7 positive. Interpreting a CK7 positive tumor is always done in the context of the patient’s clinical history and tumor location to determine the most probable source among CK7-expressing primaries.
Differential Diagnosis Using Marker Panels
Pathologists rarely rely on CK7 alone; they use it as part of an immunohistochemical panel, a group of simultaneous tests creating a unique molecular signature for the tumor. This panel approach increases the accuracy of identifying the tissue of origin compared to using a single marker. The most common companion marker is Cytokeratin 20 (CK20), expressed in the epithelial cells of the gastrointestinal tract and urothelium.
The combination of CK7 and CK20 creates four main profiles suggesting different primary sites. For example, a CK7 positive and CK20 negative (CK7+/CK20-) profile is characteristic of lung, breast, or ovarian cancers. In contrast, a CK7 negative and CK20 positive (CK7-/CK20+) profile indicates colorectal cancer.
To refine the diagnosis within the CK7 positive group, other tissue-specific markers are added to the panel. If a tumor is CK7 positive, the pathologist may test for TTF-1 (Thyroid Transcription Factor-1), which suggests a primary lung or thyroid cancer. If a breast origin is suspected, the tumor is tested for hormone receptors like Estrogen Receptor (ER). The CK7 result acts as the first filter, guiding subsequent, more specific diagnostic steps.