Guide to Staging — Melanoma

New Melanoma Staging System – By means of an unprecedented cooperative effort among cancer centers around the world, the classification system recommended by the American Joint Commission on Cancer (AJCC) has been updated as of 2010. New findings about melanoma are incorporated to provide the most accurate diagnosis and prognosis (a forecast of how the disease is likely to progress).

Formerly, very thin tumors were classified according to Clark’s level of invasion, the number of layers of skin penetrated by the tumor. In the newest staging system, Clark’s level has far less importance.

The most important factors in the new staging system are the thickness of the tumor, known as Breslow’s thickness (also called Breslow’s depth), the appearance of microscopic ulceration (meaning that the epidermis on top of a major portion of the melanoma is not intact), and mitotic rate, the speed of cell division (how fast-growing the cancer cells are). Clark’s level will enter into serious consideration only in the rare instances when mitotic rate cannot be determined.

Thin-Melanoma Thin-Melanoma-2
Two examples of thin melanomas

To be exact, Breslow’s thickness measures in millimeters (1 mm equals 0.04 inch) the distance between the upper layer of the epidermis and the deepest point of tumor penetration. The thinner the melanoma, the better the chance of a cure. Therefore, Breslow’s thickness is considered one of the most significant factors in predicting the progression of the disease.

In situ (non-invasive) melanoma remains confined to the epidermis.

• Thin tumors are less than 1.0 millimeter (mm) in Breslow’s depth.

• Intermediate tumors are 1.0-4.0 mm.

• Thick melanomas are greater than 4.0 mm.

The presence of microscopic ulceration upgrades a tumor’s seriousness and can move it into a later stage. Therefore, the physician may consider using a more aggressive treatment than would otherwise be selected. Mitotic rate has been introduced into the staging system based on recent evidence that it is also an independent factor predicting prognosis. The presence of at least one mitosis (cancer cell division) per millimeter squared (mm2) can upgrade a thin melanoma to a later stage at higher risk for metastasis.

Early Melanomas (Clinical Stages I And II)

T categories (for Tumor)

Stage Tis. The tumor is in situ and remains non-invasive in the epidermis.
Stage T1a. The tumor is invasive but less than or equal to 1.0 mm in Breslow’s thickness, without ulceration and with a mitotic rate of less than
Stage T1b. The tumor is less than or equal to 1 mm thick. It is ulcerated and/or the mitotic rate is equal to or greater than 1/mm2.
Stage T2a. The tumor is 1.01-2.0 mm thick without ulceration.
Stage T2b. The tumor is 1.01-2.0 mm thick with ulceration.
Stage T3a. The melanoma is 2.01-4.0 mm thick without ulceration.
Stage T3b. The melanoma is 2.01-4.0 mm thick with ulceration.
Stage T4a. The tumor is thicker than than 4.0 mm without ulceration
Stage T4b. The tumor is thicker than 4.0 mm with ulceration.

Later Stages

Stage III. By the time a melanoma advances to Stage III or beyond, an important change has occurred. The Breslow’s thickness is by then irrelevant and is no longer included in staging, but the presence of microscopic ulceration continues to be used, as it has an important effect on the progression of the disease. At this point, the tumor has either spread to the lymph nodes or to the skin between the primary tumor and the nearby lymph nodes. (All tissues are bathed in lymph — a colorless, watery fluid consisting mainly of white blood cells — which drains into lymphatic vessels and lymph nodes throughout the body, potentially carrying cancer cells to distant organs.)

A tumor is assigned to Stage III if it has metastasized or spread beyond the original tumor site. This can be determined by examining a biopsy of the node nearest the tumor, known as the sentinel node. Such a biopsy is now frequently done when a tumor is more than 1 mm in thickness, or when a thinner melanoma shows evidence of ulceration. As the sentinel node biopsy is not considered necessary in all cases, you may wish to discuss the matter with your physician.

In-transit or satellite metastases are also included in Stage III. In this case, the spread is to skin or underlying (subcutaneous) tissue for a distance of more than 2 centimeters (1 cm equals 0.4 inch) from the primary tumor, but not to the regional lymph nodes.

In addition, the new staging system includes metastases so tiny they can be seen only through the microscope (micrometastases). Just how advanced the tumor is into Stage III (the “N” category, for “nodes”) depends on factors such as whether the metastases are in-transit or have reached the nodes, the number of metastatic nodes, the number of cancer cells found in them, and whether or not they are micrometastases or can be seen with the naked eye.

Stage IV. The melanoma has metastasized to lymph nodes distant from the primary tumor or to internal organs, most often the lung, followed in descending order of frequency by the liver, brain, bone, and gastrointestinal tract. The two main factors in determining how advanced the melanoma is into Stage IV (the “M” category, for “metastases”) are the site of the distant metastases (nonvisceral, lung, or any other visceral metastatic sites) and elevated serum lactate dehydrogenase (LDH) level.