New, changing (evolving), or unusual nevi; the most common sign of melanoma.

Symptomatic nevi (e.g., those that itch, burn, or are painful).

An initial slow horizontal growth phase, if left untreated, is followed in months or years by a vertical growth phase (lesions that extend vertically in the skin), which indicates invasive disease and potential metastasis.

White coloration may indicate regression or scarring.

Lentigo maligna (LM) is a type of lentigo that is found on the face of elderly patients with chronically sun-damaged skin. LM is considered to be a potential precursor to melanoma (Fig. 31.35).

LM lesions are characterized by:

• a gradually enlarging tan to brown macule with irregular borders.

• slow growth over 5 to 20 years.

• an irregular color and border.

• when an LM invades the dermis, it is then referred to as a lentigo maligna melanoma (LMM). The prognosis of LMM is similar to that of other subtypes of melanoma and is dependent on the thickness of the tumor (Fig. 31.36A,B).

The lesion of a nodular melanoma may arise from a pre-existing melanocytic nevus or it may appear de novo as a nodule or plaque (Figs. 31.37 and 31.38). It occurs in 10% to 15% of patients. Because of a rapid vertical growth phase, lesions become invasive at an early stage.

Nodular melanoma lesions have the following characteristics:

• They are blue, blue-black, or nonpigmented (as in amelanotic melanoma); their color is more uniform than that of SSM.

• May ulcerate and bleed with minor trauma.

• Occur most commonly on the legs and trunk.

• May be indistinguishable from a pyogenic granuloma (see Fig. 30.52).

ALM is the least common subtype of melanoma.

Although relatively rare compared to other types of melanoma, especially in Caucasians, ALM most often appears in blacks and Asians. It is the most common subtype in people with darker skins. It is not related to sun exposure.

Lesions of ALM tend to occur on areas that do not bear hair, such as the palms, soles, and periungual skin (Figs. 31.39 and 31.40).

ALM has a tendency toward early metastasis.

A subungual ALM presenting as diffuse nail discoloration or a longitudinal pigmented band within the nail plate is potentially confused with subungual hematoma (see Fig. 22.5) or junctional nevus (Fig. 31.41). Pigment spread to the proximal or lateral nail folds (Hutchinson sign) is a hallmark of ALM (Fig. 31.42).

Five-year survival is based on the thickness of the tumor on a scale known as the Breslow measurement (Table 31.1). The thickness of the lesion is measured from the top of the granular layer of the skin to the deepest tumor cell. Melanomas that are thicker than 4 mm are associated with a high rate of distant and nodal metastasis.

Prognosis may also be determined by the grade of the melanoma, as determined by its location in the dermis using Clark levels (Table 31.2).

Sentinel lymph node status is also used for prognostication (see above).

Other important prognostic factors include the sex of the patient (women have a better prognosis than men), age (the prognosis worsens with increasing age), and the presence of ulceration or regional or distant spread.