Melanoma Pathology — Understanding Your Report

A melanoma pathology report will be scientific and could be difficult to understand. However, it will contain important information that may help indicate necessary tests, melanoma therapies and prognosis of your melanoma diagnosis. You should ask for a copy to keep in your files.

Your Pathology Report

The following factors may be present on your report:

Type of melanoma

  • Cutaneous (Acral, Nodular, Superficial Spreading, Lentigo Maligna)
  • Ocular
  • Mucosal

Breslow Thickness

Tumor thickness as defined by the Breslow's Depth of Invasion is the most important determinant of prognosis for melanoma. Increased tumor thickness is correlated with metastasis and poorer prognosis. The Breslow thickness is a better melanoma stage diagnostic indicator than the Clark’s level; it is a continuous variable and more accurate in its determinations.

The Breslow thickness is a measure (in millimeters) of the vertical depth of the tumor measured from the granular cell (very top) layer downward. An instrument called an Ocular Micrometer is used to measure the thickness of the excised tumor.

  • Tumor thickness remains the most powerful prognostic indicator that can be determined from evaluation of the primary melanoma itself. Because of the accuracy of determining outcomes, the Breslow thickness is commonly included in a melanoma diagnosis.

    Tumors are classified into four categories based on the depth:

    • Less than or equal to 0.75 mm (equivalent to Clark's Level II)
    • 0.76-1.5 mm (equivalent to Clark's Level III)
    • 1.51-4 mm (equivalent to Clark's Level IV)
    • Greater than or equal to 4 mm (equivalent to Clark's Level V)
       
  • Breslow Thickness and Survival Rate:

    • <1mm: 5-year survival is 95-100%
    • 1-2mm: 5-year survival is 80-96%
    • o 2.1-4mm: 5-year survival is 60-75%
    • >4mm: 5-year survival is 37-50%

Clark’s Level

The Clark’s level is commonly misunderstood as the melanoma stage diagnosis. The Clark’s level only refers to how deep the tumor has penetrated into the skin. Research has shown that the Clark’s level diagnosis is not a great predictor of outcome.

  • Clark's Level I - Confined to epidermis – also called “in situ” melanoma
  • Clark's Level II - Invasion of the papillary dermis (upper)
  • Clark's Level III - Filling of the papillary dermis (lower)
  • Clark's Level IV - Extending into the reticular dermis
  • Clark's Level V - Invasion of the subcutaneous tissue

Mitotic Rate

Mitotic rate is determined by counting the number of cells that are showing mitosis, or cell division. An increased mitotic rate is associated with declining survival rates. Mitotic rate is usually expressed as the number of mitoses per square millimeter.  

 

It must be noted that additional analyses have provided further insight regarding melanoma patient survival. Despite the nature of the evidence-based TNM staging system, patient age, site of primary tumor, number of sites, etc., combined with the TNM system may more accurately reflect an individual patient's outcome. The AJCC's Individualized Melanoma Patient Outcome Prediction Tools can be found online at www.melanomaprognosis.org

Other Pathology Terms

Below are a few additional terms you may encounter on a pathology report. For these and other terms, visit the MRF glossary

  • Radial Growth Phase
  • Vertical Growth Phase
  • Tumor-Infiltrating Lymphocytes
  • Ulceration
  • Regression
  • Stage of diagnosis
  • Satellites
  • Blood Vessel/Lymphatic Invasion