MAUI, HAWAII — Look for tumor mitotic rate to supplant Clark level in the forthcoming 7th edition of the American Joint Committee on Cancer melanoma staging system.
“Clark level will now only be considered for staging in the rare instances when mitotic rate is not known; otherwise it will no longer be part of the staging system,” Dr. Jeffrey E. Gershenwald said at the annual Hawaii Dermatology Seminar sponsored by Skin Disease Education Foundation.
This represents a break with the past. Within melanoma staging, Clark level enjoyed near-equal billing with tumor thickness before being downgraded in clinical relevance in the still-current 6th edition of the AJCC staging system, issued in 2002.
The 6th edition relegated Clark level to a limited role, with Clark level IV and V resulting in upstaging of thin melanomas from T1 to T1b, explained Dr. Gershenwald, vice chair of the AJCC task force charged with developing the new edition of the staging system.
The 7th edition of the AJCC melanoma staging system will be published this spring and will take effect early next year. The same changes will be made in the European staging system in coordinated fashion.
Mitotic rate will be introduced into the staging system on the basis of recent evidence suggesting that it is an independent prognostic factor. The presence of at least one mitosis per square centimeter will be sufficient to upgrade a thin melanoma from T1 to T1b.
As the AJCC staging system is rolled out, reports will be issued detailing how pathologists should determine mitotic rate, according to Dr. Gershenwald, professor of surgery at the University of Texas M.D. Anderson Cancer Center, Houston.
Clark level, he added, has caused a great deal of confusion among patients, who often confuse Clark level IV with stage IV melanoma.
“I can't tell you how many patients have come into the clinic thinking they have a stage IV melanoma and are reading their death sentence on the Internet when in fact they might very well have had a thin melanoma that happens to be Clark level IV,” he commented.
“In dialoging with your patients, please make sure they understand the difference,” Dr. Gershenwald urged.
The 7th edition of the staging system will make no major changes in the core TNM (tumor, node, metastasis) and stage grouping criteria for stages I-III melanoma. A thin melanoma will remain one that's up to 1.0 mm in thickness, and a thick one will still have to be greater than 4.0 mm. This was an evidence-based decision in response to analysis of an international database of more than 50,000 melanoma patients which validated the models utilized in the 6th edition.
There will be a few minor changes in the 6th edition having clinical relevance, however. For one, there will no longer be a lower limit as to what constitutes node-positive disease.
Also, immunohistochemical detection of nodal metastases—already in wide use in clinical practice—will for the first time become acceptable for staging purposes in the upcoming edition, Dr. Gershenwald said.
In the 7th edition, the essential elements of a pathology report for primary melanoma will be Breslow thickness, the presence or absence of ulceration, mitotic rate, and margin status.
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The 7th edition will make no major changes in the core TNM and stage grouping criteria for stages I-III melanoma. DR. GERSHENWALD
Staging, Lymph Node Assessment Are Key to Surgical Melanoma Management
The surgical management of primary melanoma varies by patient and depends in large part on key elements of the pathology report and the assessment of lymph node involvement, according to Dr. Gershenwald.
In terms of staging the disease, Breslow thickness, ulceration, mitotic rate, Clark level, and margin assessment should be considered prior to wide local excision of the tumor, he noted.
And because nodal involvement is the best predictor of recurrence and survival in melanoma, determining which patients have lymph node involvement and which patients do not is critical to the optimal management of the disease.
Lymphatic mapping together with sentinel lymph node biopsy is a relatively noninvasive way to accurately stage the regional nodal basin and enables a selective approach to regional node dissection, whereby lymphadectomy is reserved only for patients found to have pathologically documented disease, Dr. Gershenwald explained.
This combined diagnostic approach—in which a radioactive tracer is injected around the primary tumor site and a blue dye is used to identify sentinel lymph nodes to be removed for analysis—identifies regional lymph node disease that might not be seen with complete lymph node dissection and identifies patients in whom adjuvant therapy is warranted, he said.