Page 626 - Concise Pathology for Exam Preparation ( PDFDrive )

22 The Skin 611

2. Acanthosis nigricans: A pigmented skin lesion commonly present in the axillae that
may be a phenotypic marker for an underlying adenocarcinoma of the stomach.
3. Freckles: Pigmented macular lesions that occur in sun-exposed areas of the skin; they
are not premalignant and have a normal number of melanocytes along the basal cell
layer but increased melanin within individual melanocytes.
4. Lentigo simplex: It is similar to a freckle, except there are increased numbers of
melanocytes along the basal layer as well as increased melanin in each melanocyte.
5. Nevus: This denotes any congenital lesion of the skin, which has ‘nevus cells’. Nevus
cells are similar to melanocytes but differ from melanocytes in being arranged in
clusters or nests.
6. Melanocytic nevus: It is a benign neoplastic proliferation of neural crest-derived
melanocytes.
7. Junctional nevi: Contain nests of pigmented nevus cells proliferating along epidermo-
dermal junction (appear as flat, pigmented lesions).
8. Junctional nevi usually develop into compound nevi, as nevus cells extend into the
underlying superficial dermis, forming cords and columns of cells; so that both a junc-
tional and an intradermal component is present (raised, pigmented and verruca-like
lesions).
9. Intradermal nevus, which is the most common type of nevus in adults, is located in
the upper dermis.
10. Dysplastic nevi may be a part of the dysplastic nevus syndrome; and they may be
precursor lesions of malignant melanoma.

Malignant Melanoma
• It is a malignant tumour derived from melanocytes.
• Both sexes are affected equally; it is more common in whites than in African-Americans,
and has a predilection for fair-skinned people.
• Exposure to excessive sunlight at an early age is the single most important predisposing
risk factor. Other risk factors include a history of severe sunburn, dysplastic nevus syn-
drome, melanoma in a first- or second-degree relative and xeroderma pigmentosum.
• About 10–15% melanomas have genetic abnormalities. Most common aberrations are
mutations in CDKN2A, RB and PTEN genes. Activating mutations in NRAS and BRAF
are also implicated.
• Symptoms such as bleeding, itching, ulceration and pain in a pigmented lesion warrant
evaluation. The following signs are indicative of development of malignancy in a pre-
existing lesion:
• Asymmetry: One half of the lesion does not match the other half.
• Border irregularity: The edges are ragged, notched or blurred.
• Colour variation: Pigmentation is not uniform and may display shades of tan, brown
or black; white, reddish or blue discolouration is of particular concern.
• Diameter: A diameter greater than 6 mm is characteristic, although some melanomas
may have smaller diameters; any growth in a nevus warrants an evaluation.
• Evolving: Changes in the lesion over time are characteristic; this factor is critical for
nodular or amelanotic (nonpigmented) melanoma, which may not exhibit the classic
criteria above.
• Most variants have an initial radial growth phase in which malignant melanocytes
proliferate laterally within the epidermis, along the dermoepidermal junction or within
the papillary dermis; metastasis cannot occur in this phase.
• There may be a vertical growth phase in which malignant cells penetrate the underly-
ing reticular dermis; metastasis can occur in this phase.
• Tumour cells are polygonal to spindled, larger than normal melanocytes, have atypical
nuclei showing irregular contours and prominent eosinophilic nucleoli. Intracytoplas-
mic melanin is usually seen. Tumours not showing pigment are called amelanotic mela-
nomas (Fig. 22.3). Various patterns of growth of tumour cells may be seen including
solid sheets, islands, glands, etc.
• The superficial spreading melanoma is the most common type and primarily affects
women over 50 years of age. The lower extremities and back are the most common
locations. Histologically, it is characterized by pagetoid infiltration of the epidermis by
atypical melanocytes.
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