Diagnosis

The diagnosis of Merkel Cell Carcinoma is made with a skin biopsy, which is examined under the microscope. Common types of biopsy include a punch (a small core is taken) or a shave (part of the top of the lesion is removed with a scalpel). The pathologist will then use special studies (called immunohistochemistry stains) to determine if a lesion is an Merkel Cell Carcinoma or another form of cancer, such as small cell lung cancer (SCLC), lymphoma, or melanoma. Each of these cancers has unique characteristics when examined with such special stains.

Merkel Cell Carcinoma can travel from the skin, through the lymphatic vessels, to the sentinel lymph node. The sentinel lymph node is the first lymph node that connects with the part of the body where the cancer arose. If a lymph node feels enlarged, it may contain Merkel Cell Carcinoma (macrometastases). Sometimes, lymph nodes may contain Merkel Cell Carcinoma, but feel normal and not feel enlarged (micrometastases).

There is a technique to identify the sentinel lymph node when it cannot be felt on physical exam. A blue dye and or a radioactive tracer are injected at the site of the primary lesion. Within 5 to 10 minutes, the dye and tracer travel along the same path that cancer cells would spread through the lymphatic vessels and collect in the sentinel lymph node. An instrument that detects the tracer is used to map the path from the skin to the sentinel lymph node. The sentinel lymph node is removed and examined for the presence of Merkel Cell Carcinoma under a microscope. If Merkel Cell Carcinoma is not found in the sentinel lymph node, then the chance that it has spread elsewhere in the body is lower than if Merkel Cell Carcinoma was found.

This technique has a low risk of significant side effects, provides useful information on the chance of spread, and identifies the lymph node region containing the sentinel lymph node (draining lymph node basin), which is sometimes difficult, especially for lesions on the head and neck.