Definition:

stage I melanomalisten (... MEH-luh-NOH-muh)

Stage I is divided into stages IA and IB. In stage IA, the tumor is not more than 1 millimeter thick, with no ulceration (a break in the skin). In stage IB, (1) the tumor is not more than 1 millimeter thick and it has ulceration; or (2) the tumor is more than 1 but not more than 2 millimeters thick, with no ulceration.

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Two-panel drawing of stage I melanoma. The first panel shows a stage IA tumor that is not more than 1 millimeter thick, with no ulceration (break in the skin). The second panel shows two stage IB tumors. One tumor is not more than 1 millimeter thick, with ulceration, and the other tumor is more than 1 but not more than 2 millimeters thick, with no ulceration. Also shown are the epidermis (outer layer of the skin), the dermis (inner layer of the skin), and the subcutaneous tissue below the dermis.