Chapter 18: Nevi and Melanoma

INTRODUCTION TO CHAPTER

Melanocytic nevi (moles) are common benign skin tumors. In most people, these are primarily of cosmetic significance. However, nevi can occasionally become irritated or subjected to trauma and may need to be removed. Most nevi are benign, but, atypical nevi have some features that resemble malignant melanoma, and in certain circumstances the presence of atypical nevi is a marker for an increased risk of developing malignant melanoma.

Melanoma is a potentially deadly cancer whose incidence is on the rise. It is unique among most serious cancers, because it can be detected by both patients and clinicians with a simple skin examination. The clinician can provide a great service to patients by providing a few simple guidelines for the early detection of melanoma.

ACQUIRED MELANOCYTIC NEVI

Introduction

Melanocytic nevi (moles) are among the most common benign tumors in humans. Nevi are more common in Caucasians. They are less common in Asians and Black individuals. But when they do occur they are more likely to be on the palms and soles. Interestingly, nevi are also less common in patients with the melanocortin-1 receptor (MC1-R) gene pigment variant (red hair, fair skin, always burns).

Nevi appear in early childhood reaching a maximum number in the 3rd to 4th decade of life, with a subsequent decline in number.¹ They are more common on sun-exposed skin, as natural sunlight and artificial ultraviolet light are factors in their induction.

Pathophysiology

Nevi are benign hamartomas of melanocytic nevus cells. They are thought to arise from cells delivered from the neural crest to the skin during embryologic development.

Clinical Presentation

History

Nevi are usually asymptomatic. Patients may bring nevi to a clinician's attention because of new onset, growth, symptoms of pain or itch, interference with activities of daily living, or alarming appearance. They may also bring them to attention because of a cosmetically unacceptable appearance.

Physical Examination

Nevi are small, circumscribed macules, papules, or nodules. They range in color from blue/black through brown, pink to skin colored. Acquired nevi are almost always less than 1 cm in diameter. Melanocytic lesions greater than 1 cm may be congenital nevi, atypical nevi, or melanoma. Nevi may occur anywhere but there is a predilection to sun-exposed skin.

Common presentations of nevi:

• Junctional nevi arise at the skin dermal–epidermal junction; they are typically macular (Figure 18-1).

• Intradermal nevi present with nevus cells confined to the dermis of the skin and are papular (Figure 18-2).

• Compound nevi have both junctional and dermal components and are usually papular.