What are Clark Levels?

Clark levels are a staging classification system that has been historically used in melanoma.

How are Clark levels used in melanoma diagnosis?

The Clark level refers to the depth of involvement of the layers of the skin, or the vertical growth into the skin levels. The different Clark levels are:

  • Level I: the melanoma is only in the outermost layer of the skin, the epidermis
  • Level II: the melanoma has grown into the second layer of the skin, the papillary dermis
  • Level III: the melanoma has filled the papillary dermis and has grown into the area between the papillary dermis and the reticular dermis, known as the papillary-reticular dermal interface
  • Level IV: the melanoma has spread into the reticular dermis
  • Level V: the melanoma has invaded the subcutaneous tissue1,2

Updated classification to staging melanoma

The American Joint Committee on Cancer (AJCC) has developed updated guidelines on melanoma classification based on evidence and cooperation from several major cancer centers. Their newest guidelines, the eighth edition, won’t be available publicly until 2018, and they advise that all cancers newly diagnosed through December 2017 should follow the seventh edition of the guidelines, which were published in 2010. The AJCC guidelines classify melanomas based on:

  • Tumor size (T)
  • Lymph node involvement (N)
  • Metastasis (M), or the spread of the cancer into other tissues or organs

Each of these components is further classified using numbers to note the level of invovlement:

  • T1: melanomas 1.0 mm or less in thickness
  • T2: melanomas 1.01-2.0 mm
  • T3: melanomas 2.01-4.0 mm
  • T4: melanomas more than 4.0 mm
  • N0: no regional lymph nodes involved
  • N1: one regional lymph node is involved
  • N2: 2-3 lymph nodes are involved
  • N3: 4 or more lymph nodes are involved
  • M0: no detectable metastases
  • M1a: the cancer has spread (metastasized) to the skin, subcutaneous, or distant lymph nodes
  • M1b: there are metastases to the lung
  • M1c: any metastases to all other distant sites combined with an elevated serum LDH

The different components and numbers are then classified into cancer stages (Stage I-IV).3

Melanomas – early detection is key

Whether using Clark levels or the AJCC classification system, early detection of melanoma is key to increasing survival. Melanoma is the most dangerous form of skin cancer and is the cause of death of an estimated 10,130 people in the U.S. each year. When melanoma is detected and treated early, it is almost always curable.

Melanomas are named for the pigment-producing cells in which they develop, the melanocytes. Melanomas are most often caused by intense exposure to UV (ultraviolet) light, whether from the sun or artificial means, like tanning beds. The ABCDE signs of melanoma are the best way to identify these skin cancers early:

  • A – Asymmetry, where one half of the mole is different than the other half
  • B – Border, where the border isn’t a clean line but may be scalloped, irregular, or poorly defined
  • C – Color, where the color of the mole varies from one area to another
  • D – Diameter, most melanomas are greater than 6 mm (equal to the size of a pencil eraser), although they can be smaller
  • E – Evolving, which notes changes that occur in the size, shape, or color of a mole over time

If you notice any spots that meet the ABCDE criteria or that are changing, itching, or bleeding, you should make an appointment with a doctor or dermatologist right away.4

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