What is a flat mole?

Flat Mole Description and Characteristics

A flat mole is a pigmented skin lesion that lacks elevation and appears level with the surrounding skin surface, characterized by its non-palpable nature and potential for irregular margins and pigmentation. 1

Clinical Features of Flat Moles

• Elevation: Flat moles are non-palpable and level with the surrounding skin, in contrast to raised or nodular moles 1
• Size: Typically measured by maximum diameter, with atypical flat moles often being 6 mm or larger 2, 3
• Color: May display uniform or variegated pigmentation, with multiple colors potentially indicating atypical features 1
• Border: Can have regular or irregular margins, with irregularity being a concerning feature 1
• Surface texture: Smooth surface without the pebbled texture sometimes seen in raised moles 2

Types of Flat Moles

• Junctional nevus: A common type of flat mole where nevomelanocytes (mole cells) are located at the junction between the epidermis and dermis 4
• Lentigo maligna: A specific type of flat pigmented lesion that represents melanoma in situ, commonly found on sun-exposed areas of the face in older individuals 1, 5
• Common acquired melanocytic nevi: These begin appearing around age 1 and peak in number during the second or third decades of life 4

Clinical Assessment of Flat Moles

When examining a flat mole, clinicians should document:

• Duration: How long the lesion has been present 1
• Changes: Any alterations in size, color, or shape 1
• Symptoms: Presence of itching, bleeding, or other symptoms 1
• Site: Anatomical location of the lesion 1
• Size: Maximum diameter measurement 1
• Description: Noting irregular margins, irregular pigmentation, and flat appearance 1

Warning Signs for Flat Moles

Concerning features that warrant further evaluation include:

• Asymmetry: Uneven or irregular shape 2
• Border irregularity: Poorly defined or notched edges 2
• Color variegation: Multiple colors within the same lesion 2
• Diameter: Size greater than 6 mm 2
• Evolution: Any changes in appearance over time 2
• "Ugly duckling" sign: A flat mole that looks different from other moles on the same person 2

Risk Assessment

• The annual transformation rate of any single mole into melanoma is extremely low, ranging from 0.0005% or less for individuals younger than 40 years to 0.003% for men older than 60 years 6
• Flat moles with atypical features may indicate higher melanoma risk, particularly in individuals with multiple atypical moles and family history of melanoma 3
• Lentigo maligna, a flat pigmented lesion on sun-exposed skin, represents melanoma in situ and requires complete excision with clear histological margins 1, 5

Management Considerations

• Flat moles with suspicious features should be referred urgently to a dermatologist or surgeon with expertise in pigmented lesions 5
• Excisional biopsy is preferred for suspicious flat moles, as shave and punch biopsies can make pathological staging impossible 5
• For elderly patients with lentigo maligna where complete excision is impossible or contraindicated, alternative options include radiotherapy, CO2 laser, and cryotherapy 5

Common Pitfalls

• Underestimating the extent of flat pigmented lesions, particularly lentigo maligna on the face, can lead to incomplete excision and recurrence 5
• Partial removal of flat melanocytic lesions can result in pseudomelanoma, causing diagnostic confusion 5
• Prophylactic excision of all flat pigmented lesions without suspicious features is not recommended as it is neither clinically beneficial nor cost-effective 2, 3