What is atypical junctional melanocytic (melanocyte) hyperplasia?

From the Guidelines

Atypical junctional melanocytic hyperplasia requires complete surgical excision with narrow margins, typically 0.5- to 1-cm, to prevent progression to melanoma, as recommended by the guidelines of care for the management of primary cutaneous melanoma 1. This condition represents an abnormal proliferation of melanocytes at the junction between the epidermis and dermis with some atypical features, but not enough to diagnose melanoma. After diagnosis via biopsy, patients should undergo complete excision followed by regular skin examinations every 3-6 months for the first year, then annually thereafter. Some key points to consider in the management of atypical junctional melanocytic hyperplasia include:

• The use of narrow surgical margins, such as 0.5- to 1-cm, which is generally adequate and associated with low recurrence rates for MIS, non-LM types, and for most MIS on the trunk and extremities 1.
• The importance of complete excision, which may necessitate the use of wider surgical margins and/or margin control techniques that allow comprehensive histologic assessment of the peripheral margins, especially for certain MIS subtypes (LM and acral lentiginous) that tend to have a higher propensity for subclinical peripheral tumor extension and/or adjacent multifocal microscopic disease 1.
• The need for microscopic assessment of the lesion, which can be complicated by the presence of sun-damaged melanocytes (actinic melanocytic hyperplasia), and may require expert opinion and sampling of representative sun-damaged skin 1. Patients should also practice monthly self-skin examinations and use sun protection measures including broad-spectrum sunscreen (SPF 30+), protective clothing, and avoiding peak sun hours (10am-4pm). Atypical junctional melanocytic hyperplasia carries an increased risk for developing melanoma either at the same site if incompletely removed or elsewhere on the body, as it may indicate a predisposition to melanocytic neoplasia. The condition is thought to result from a combination of genetic factors and ultraviolet radiation damage, which causes DNA mutations in melanocytes leading to abnormal growth patterns.

From the Research

Definition and Characteristics

• Atypical junctional melanocytic hyperplasia is a benign condition characterized by an abnormal proliferation of melanocytes at the dermoepidermal junction 2.
• It is often associated with intradermal nevi and can be confused with melanoma in situ due to its atypical histological features 2.
• The condition is relatively common, with a frequency of 6.2% in a study of 400 intradermal nevi cases 2.

Histological Features

• The lesions are typically dome-shaped with an intradermal component consisting of conventional nevus cells 2.
• The melanocytes exhibit abundant pale to clear cytoplasm, an increased nuclear:cytoplasmic ratio, and often prominent nucleoli 2.
• The absence of features such as lateral spread, upward epidermal migration, marked cytologic atypia, finely granular "smoky" melanin pigment, mitotic figures, and a subjacent host inflammatory response can help distinguish atypical junctional melanocytic hyperplasia from melanoma in situ 2.

Association with Melanoma

• Atypical junctional melanocytic hyperplasia has been found to be associated with melanomas, with a significant frequency of 55.7% in melanoma excisions compared to 24.8% in non-melanoma cutaneous tumor excisions 3.
• The association between atypical junctional melanocytic hyperplasia and melanoma remains significant even after controlling for solar elastosis 3.
• The biological potential of atypical junctional melanocytic hyperplasia at the periphery of melanomas is uncertain, with some studies suggesting it may be a field of melanocytic dysplasia associated with melanoma in situ 3, 4.

Diagnostic Challenges

• Differentiating atypical junctional melanocytic hyperplasia from melanoma in situ or other melanocytic lesions can be challenging due to overlapping histological features 4, 5.
• Melanocyte density has been found to be a useful objective criterion for distinguishing atypical junctional melanocytic hyperplasia from melanoma in situ, with a statistically significant difference between the two conditions 4.
• Clinical and pathological correlation, as well as the use of ancillary studies, may be necessary to establish a definitive diagnosis and guide treatment decisions 6.