How is Merkel cell carcinoma diagnosed and staged?

The doctor may use the following procedures and tests to diagnose MCC. Some of these tests are also used to help determine the stage of the disease. Stage is a description of the extent of cancer.
A biopsy is the removal of cells or tissue from a tumor for examination by a pathologist. The pathologist may study tissue samples under a microscope or perform other tests on the cells or tissue. Biopsies are used for both diagnosis and staging. The surgeon may also remove lymph nodes (small, round organs that trap cancer cells, bacteria, or other harmful substances) to help determine the stage of the disease.
Sentinel lymph node (SLN) biopsy is a procedure in which the sentinel lymph node is removed and examined under a microscope to determine whether cancer cells are present. The sentinel lymph node is the first lymph node to which cancer is likely to spread from the primary tumor. SLN biopsy is used to help determine the stage of the disease. SLN biopsy may cause fewer side effects than standard lymph node removal because fewer lymph nodes are taken out.
Immunohistochemistry (staining of cells with agents that react with antibodies on the surface of cancer cells) is a laboratory technique used to tell the difference between MCC and other types of cancer (2).
Computed tomography (CT), a procedure that uses special x-ray equipment to obtain cross-sectional pictures of the body, can distinguish MCC from small cell lung cancer and show whether the disease has metastasized (spread) to other parts of the body (5).
In an octreotide scan (sometimes called Somatostatin Receptor Scintigraphy or SRS), the doctor injects a small amount of a radioactive drug into a vein. The drug travels through the bloodstream and attaches to tumor cells. A machine called a scanner detects the radioactive material and creates scans (pictures) showing where the tumor cells are located in the body. For MCC, this test can be used for both diagnosis and staging (5).
A PET scan uses radioactive sugar, which is absorbed by cancer cells and appears as dark areas on the scan. It can be used for both diagnosis and staging of MCC.