Nests of melanocytes, predominantly in rete ridges

On path: remember to evaluate size, symmetry, circumscription; need full lesion (shave or excision)

Aka Clark’s nevus

On path, these characteristics may be seen:

Other atypical features include asymmetry, poor circumscription, Pagetoid spread

Recent description of nevi with features of Spitz and dysplastic (Clark’s) nevi was called “Spark’s nevus”

In general, dysplastic nevi are not considered premalignant lesions. They represent a patient risk factor for melanoma and are re-excised less because of concern that they will evolve into a melanoma and more because of concern that a melanoma diagnosis was missed.

Typically, DNs are reported as having mild, moderate, or severe atypia; the risk of melanomas being misclassified as mild or moderate DNs appears to be extremely small to none. Severe DNs are uniformly re-excised (as they are borderline to MMIS). However, many are comfortable (and some evidence supports) not re-excising mild and moderate DNs, especially if margins were clear on biopsy.

Small <1.5 cm, Medium = 1.5–20 cm

Large/giant >20 cm (or >5 % TBSA in prepubertal), can have “bathing trunk” distribution

Path: “congenital pattern” = wraps around adnexal structures

Increased risk of MM, neurocutaneous melanosis (NCM) = syndrome of large congenital melanocytic nevi with meningeal melanosis or melanoma

Greatest risk for NCM in axial lesions with satellite nevi, screen with MRI

50 % with NCM get leptomeningeal MM

Aka “benign juvenile melanoma”

In kids, clinical ddx JXG, mastocytoma

Dermoscopy: starburst pattern

Path: circumscribed elongated nests (may look like bananas), separated from adjacent keratinocytes (clefting around nests), with Kamino bodies (pink globules)

Many Spitz have HRAS mutation associated

“Spitzoid features” of other nevi include: nests that are vertical, epithelioid appearance, spindle cells

Classically a recently developed well-circumscribed black lesion on thigh of young woman (without other pigmented lesions on body)

Some classify this as a subtype of Spitz nevus

Path: fascicles of uniform, slender spindle cells with melanin

Aka plexiform spindle cell nevus

Dark papule/nodule typically on head/neck in first few decades

Path: sharply demarcated wedge-shaped pigmented proliferation

Shares features with both Spitz nevi and blue nevi, and can mimic melanoma

A nevus with a surrounding white halo, caused by an immune response to nevus cells (infiltrating lymphocytes on path); repigments if remove nevus

Variant of nevus with predominance of altered, large melanocytes with vacuolated cytoplasm

Unilateral, hyperpigmented patch, often with hypertrichosis

On path, acanthosis, features of smooth muscle hamartoma, basilar hyperpigmentation; ddx accessory nipple (papillomatous)

Speckled lentiginous nevus

Can see in phakomatosis pigmentovascularis (with capillary malformation), phakomatosis pigmentokeratotica (with nevus sebaceus)

Increased number of melanocytes and melanin (but not a neoplastic proliferation)

Essentially the same as café-au-lait macules, but <5 mm

Labial lentigo: path = mucosal, ectatic, broad rete ridges, basilar hyperpigmentation

Essentially the same as lentigines, but >5 mm

Path: increased melanin/melanosomes, but not increased melanocytes

See in older patients; may be precursors for macular seborrheic keratoses

From UV exposure

Path: club-shaped rete ridges with pigmentation, solar elastosis

Only in sun-exposed areas, can see in kids

Melanoma represents less than 2 % of skin cancers, but accounts for the majority of skin cancer deaths (about 10,000/year)

Sixth most common cancer diagnosis in US and the most common cancer in Caucasian women age 25–29

Path: atypical features as described in dysplastic nevi, neoplastic proliferation of melanocytes beyond nests, Pagetoid spread, artifactual splitting in epidermis from lack of cellular adhesions (desmosomes) with melanocyte infiltrate, regression

Risk factors include: exposure to sun (intermittent sun exposure significant rather than total sun exposure seems more important), use of sun beds/tanning bed, skin phenotype/pigmentation (Fitzpatrick skin type), number of melanocytic nevi and dysplastic nevi, family history of melanoma, personal history of melanoma

Despite association of melanoma with ultraviolet radiation (exemplified by xeroderma pigmentosum with defects in nucleotide excision repair), it is not clear how UVR causes melanoma; melanomas lack the UVB signature mutations seen in NMSCs. It is clear, however, that melanoma can occur without sun exposure.

Most melanomas occur de novo; less than 1/4 in association with nevi; dysplastic nevi no more likely to develop MM than other common nevi

Breslow depth (from top of granular layer to deepest point) relates to prognosis; Clark level was another measure of depth that was found to be poorly reproducible and thus has fallen out of favor

Hutchinson’s sign = melanonychia with pigment on proximal nail fold, suggestive of melanoma

2010 AJCC criteria (T/N/M staging):

60–70 % of melanomas

No radial growth phase, 15–30 %

5–10 %

Noted in darker skin patients, not because increased incidence, but all other types decreased incidence

5–15 %, slow growing on sun-exposed skin

Ddx pyogenic granuloma, BCC, SCC, purple plums

May have worse prognosis, but also often with delays in diagnosis

May have tendency to locally recur, but less likely to metastasize

Melanocytes found in the posterior uveal tract; posterior uveal chamber MM can metastasize to liver (hematogenous spread)

Includes lentigo maligna

A papule or nodule, often on palms/soles, can be on scalp

Clinical ddx: pyogenic granuloma, amelanotic melanoma

Path: downward grown of blue basaloid cells with ducts

Three benign variants (and one malignant):

Typically around eyes, but can be on abdomen/thighs/genitals

Path: multiple small ducts in fibrous stroma, nests may resemble commas or tadpoles

Can be eruptive in Down syndrome

Variants include:

In the painful tumor ddx

Actually thought to be apocrine-derived by most now

Clinical: “turban tumors”

Path: “jigsaw puzzle,” well-circumscribed pieces, two cell populations, glassy rim

Related to cylindromas; can see in Brooke-Spiegler

Path: Round “blue balls” in the dermis, but not as well circumscribed as jigsaw of cylindroma; 3 cell types = 1. pale, 2. dark, and 3. lymphocytes (this may be why it is painful)

Seen in vulvar and perianal areas

Path = partially cystic with papillary and glandular areas, no epidermal connection

Path = dilated apocrine gland on eyelid skin, shows decapitation secretion, lined by two layers of cells

Most commonly occurs on the upper lip, locally aggressive

Path: poorly circumscribed, deeply infiltrative (subcutaneous to even muscle) with perineural invasion

Most commonly in groin, perianal, scrotum, vulva

25–50 % associated with cutaneous malignancy

Path = atypical cells with abundant pale cytoplasm, can see Pagetoid spread

Yellow delled papules on face/chest

Path: large sebaceous lobules grouped around a central dilated duct (all connected to hair follicle)

The hallmark lesion of Muir-Torre syndrome (MLH1, MSH2 defect)

Path: multiple sharply demarcated sebaceous lobules, separated and compressed connective tissue septa; classically, approximately half of the cells are mature sebocytes.

On a spectrum with sebaceous adenoma (some controversy about how to distinguish), may be associated with Muir-Torre

Path: similar to sebaceous adenoma, classically with a majority of sebocytes undifferentiated/germinative and only scattered clusters of mature sebocytes

Classically on eyelid, though BCC more likely in this location

Path: may see Pagetoid spread

Sebaceous neoplasms (adenoma = defining, epithelioma, or carcinoma), keratoacanthomas, and internal malignancies