A Guide to Adult Melanocytic Lesions and Mimickers

Primary Care Clinicians (PCPs) on RubiconMD frequently utilize our Dermatology panel to learn how to evaluate, monitor, and manage skin lesions.

This week, we hosted a Continuing Medical Education (CME) webinar led by Dr. JiaDe (Jeff) Yu, Assistant Professor of Dermatology at Massachusetts General Hospital (MGH) and Harvard Medical School. He is also the Director of Contact and Occupational Dermatitis Clinic with a special clinical interest in pediatric allergic contact dermatitis. Dr. Yu was kind enough to educate webinar attendees on various melanocytic lesions, and the benign mimickers PCPs may encounter when treating their patients.

We summarized Dr. Yu’s insights below - be sure to watch the webinar here for all the details, photos, and tips shared:

1. Basic definitions and terminology: What is a melanocyte? A nevus? What is their basic anatomy and where do they live on the skin?

Melanocytes are cells that contain melanin producing organelles called melanosomes. Melanin is transported to keratinocytes and helps protect the body against UV damage and contribute to skin’s color. Everyone has the same number of melanocytes, but the amount of melanin is different (1). With this background in mind, melanocytic lesions occur when there is an increase in the number of melanocytes.

A nevus is a birthmark or a mole on the skin, that may or may not be melanocytic. 

Benign nevi can be anywhere on the skin. They are typically well-circumscribed, round, and symmetric. Other things to note is that it is normal to have hair coming out of them, as this indicates the underlying skin is acting normally. Benign nevi are not symptomatic or painful, and may change over time - but beware if new moles or nevi occur after the age of 30. 

2.What are some examples of benign melanocytic lesions in adults? 

Examples are benign lesions include:

  • Junctional Nevus: identified as flat, sharply defined borders, and symmetric.
  • Compound Nevus: identified as raised, sharp borders, symmetric, and may grow hair.
  • Dermal Nevus: identified as raised, pink or brown in color, typically fleshy and soft, with little to no pigment.
  • Blue Nevus: identified well circumscribed blue or blue-gray dome shaped papules - these are typically benign but can rarely have a malignant transformation.
  • Acral Nevus: identified as flat - the benign acral nevus will have parallel furrows, with most pigmentation occurring there. It is important to note that there is acral melanoma, distinguished by parallel ridges or raised patterns in the skin. Dr. Yu shared his tip for remembering the difference with the saying  “ridge = risky and furrow = fine.”
3. What is melanoma’s prevalence? What are some examples of malignant melanocytic lesions in adults?

Melanoma is becoming more common in white adults, with 1/70 developing melanoma at some point in their lives. This accounts for only 1% of cancer deaths, but the majority of skin cancer related deaths (2). While more melanoma is being detected, deaths are remaining stable.

Dr. Yu shared two tactics to screen for melanoma, the ABCDE training method - which asks clinicians to look for asymmetry, borders, color, diameter, and evolution of a nevus. Additionally, he recommends utilizing the ‘ugly duckling’ method to flag moles that do not look like other moles on the body as suspicious. 

Examples are malignant lesions include:

  • Nodular Melanoma: identified as a raised bump that grows quickly, often without ulceration. These are thicker in their most advanced stages.
  • Lentigo Maligna Melanoma: identified on the face, nose, or cheek in sun-damaged individuals, and typically occurs in older adults over 70.
  • Acral Lentiginous Melanoma: identified on the hands, nails, and feet and accounts for a majority of melanoma cases in African-Americans and Asian-Americans.
  • Amelanotic Melanoma: known to be difficult to diagnosis, typically raised and pink or fleshy in color

See figure below for reference (3):

4. What are some examples of melanocytic mimickers in adults?

Examples of melanocytic mimickers include:

  • Seborrheic Keratosis: identified as benign, cutaneous lesions that occur after the age of 30 - these are typically textured, almost crusty lesions on the skin.
  • Dermatofibroma: identified as hyperpigmented, firm papules that give off a dimple appearance.
  • Cherry Angioma: identified as bright red proliferations that occur after the age of 30. These can sometimes be darker in pigment and related to hormone changes (pregnancy, for example).  


Dr. Yu emphasized that accurate sampling is vital to a correct diagnosis. While excisional biopsy is an ideal way of sampling the lesion, time and cost considerations may limit the applicability of this method. Instead, saucerization or ‘deep shave biopsies’ are the most common and preferred method. Dr. Yu advises to sample the whole lesion if possible, because it decreases the likelihood of a sampling error.

While it is not always possible, Dr. Yu shared a mantra ‘when in doubt, cut it out’ to ensure any lesions are properly evaluated and acted on for patients.

For full access to this Dermatology webinar, as well as past CME webinars, please visit rubiconmd.com/cme.



  1. https://www.webmd.com/a-to-z-guides/what-is-melanin#1
  2. https://www.cancer.net/cancer-types/melanoma/statistics
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3625372/