Stage I melanoma is defined as a melanoma that is up to 2 mm thick. A Stage I melanoma may or may not have ulceration. There is no evidence the cancer has spread to lymph nodes or distant sites (metastasis). There are two subclasses of Stage I melanoma: 1A, 1B.

Stage I Melanomas Are Defined by 2 Primary Characteristics: 

• Tumor thickness (Breslow Depth): how deeply the tumor has penetrated the skin. Thickness is measured in millimeters (mm). For example:

  • 1 mm = .04 inch, or less than 1/16 inch (about equal to the edge of a penny)

  • 2 mm = between 1/16 and 1/8 inch (about equal to the edge of a nickel)

  • 4 mm = between 1/8 and 1/4 inch (about equal to the edges of two nickels)

• Ulceration: when the epidermis (or top layer of skin)  that covers a portion of the primary melanoma is not intact. Ulceration can only be seen under a microscope, not by the naked eye.

Note: Clark level is a secondary characteristic used for Stage I melanomas where the primary tumor is no more than 1 mm thick. It measures the depth of invasion according to the number of layers of skin the tumor has penetrated.

There Are 2 Subclasses of Stage I Melanoma

Stage 1A (T1aN0M0)

T1a: Tumor is no more than 1.0 mm thick, no ulceration

Clark level of II or III

N0 = No spread to nearby lymph nodes

M0 = No evidence of metastasis to distant sites

Stage IB (T1bN0M0 or T2bN0M0)

T1b: tumor is no more than 1mm thick, no ulceration

Clark Level of IV or V

T2a: tumor is 1.0 -2mm thick with no ulceration

N0 = No spread to nearby lymph nodes

M0 = No evidence of metastasis to distant sites

Risk: Patients with Stage I Melanoma are considered low risk for local recurrence or for regional and distant metastases. Keep in mind that the statistics shown for survival are averages; everyone's cancer and survival rate is based on many factors and determined on an individual basis.

For more information, see Stage I Follow-up.