My patient presents for evaluation of a mole on her arm. What features of the mole should I look for to help me distinguish a benign mole from melanoma?

Great question! Identifying a melanoma is a lot easier than you might think. A good starting point is the ABCDE criteria, which stands for Asymmetry, Border irregularity, Color variation, Diameter > 6 mm/Dark, and Evolution over time (see Fig 1 below). 1 Higher number of these characteristics in a particular lesion increases the probability of it being melanoma. For example, in the presence of just one characteristic, the positive likelihood ratio (LR) is 1.5 with the probability of melanoma of 7.4%. However, if all five characteristics are present, the positive LR rises to 107, while the probability of melanoma increases to 85%. 2,3,4

Another useful trick is looking for the “ugly duckling sign” (UDS), which refers to any pigmented lesion that appears obviously different than others on a patient’s body.5 For example, let’s say you’re seeing a patient with multiple small, circular, equally-sized moles on his forearm. A few inches away, he has a significantly larger mole with an irregular border. This would qualify as a positive UDS.  While the sensitivities of melanoma recognition are similar for the UDS and the ABCDE criteria (100% and 99%, respectively), the UDS has been shown to significantly improve specificity (88.3%) and accuracy (90.9%) when compared to the ABCDE criteria alone (57.4% and 66.7 %, respectively).6 So incorporating both sets of criteria into your approach to melanoma recognition may be prudent.

Once you suspect a melanoma, your should refer your patient to a dermatologist for an excisional biopsy, the gold standard for melanoma diagnosis.  This procedure consists of excising the entire lesion with 1-3 mm margins.7 The resulting sample can then be used to histologically confirm the diagnosis, prognosticate, and guide management.

Primary care providers play a crucial role in the early detection and treatment of melanoma, so keep your eyes open for any “unusual” looking moles, even if you’re seeing a patient for something unrelated!

Bonus Pearl

Did you know that cardiac involvement with melanoma is not uncommon, affecting an estimated 28% to 56% of patients with metastatic melanoma? 8


Figure 1: ABCDE criteria to help differentiate benign skin lesions from melanoma


 From Pawan Sonawane, Sahel Shardhul, Raju Mendhe, “Cloud based mobile solution for early detection of Skin Cancer using Artificial Intelligence”, International Journal of Scientific Research in Computer Science, Engineering and Information Technology (IJSRCSEIT), ISSN : 2456-3307, Volume 7 Issue 3, pp. 312-324, May-June 2021. Available at doi : Journal URL : (

Contributed by Aditya Nellore, 4th year Medical Student, St. Louis University Medical School, St. Louis, Missouri

Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.



  1. Goldsmith SM. Why Is Darkness an Essential Feature for Melanoma Recognition? Skinmed. 2021 Oct 1;19(5):334-336. PMID: 34861912. (
  2. Duarte AF, Sousa-Pinto B, Azevedo LF, Barros AM, Puig S, Malvehy J, Haneke E, Correia O. Clinical ABCDE rule for early melanoma detection. Eur J Dermatol. 2021 Dec 1;31(6):771-778. doi: 10.1684/ejd.2021.4171. PMID: 35107069. (
  3. Thomas L, Tranchand P, Berard F, Secchi T, Colin C, Moulin G. Semiological value of ABCDE criteria in the diagnosis of cutaneous pigmented tumors. Dermatology. 1998;197(1):11-7. doi: 10.1159/000017969. PMID: 9693179. (
  4. Ebell M. Clinical diagnosis of melanoma. Am Fam Physician. 2008 Nov 15;78(10):1205, 1208. PMID: 19035070. (
  5. Gaudy-Marqueste C, Wazaefi Y, Bruneu Y, Triller R, Thomas L, Pellacani G, Malvehy J, Avril MF, Monestier S, Richard MA, Fertil B, Grob JJ. Ugly Duckling Sign as a Major Factor of Efficiency in Melanoma Detection. JAMA Dermatol. 2017 Apr 1;153(4):279-284. doi: 10.1001/jamadermatol.2016.5500. PMID: 28196213. (
  6. Ilyas M, Costello CM, Zhang N, Sharma A. The role of the ugly duckling sign in patient education. J Am Acad Dermatol. 2017 Dec;77(6):1088-1095. doi: 10.1016/j.jaad.2017.06.152. Epub 2017 Sep 28. PMID: 28964538. (
  7. Swetter SM, Tsao H, Bichakjian CK, Curiel-Lewandrowski C, Elder DE, Gershenwald JE, Guild V, Grant-Kels JM, Halpern AC, Johnson TM, Sober AJ, Thompson JA, Wisco OJ, Wyatt S, Hu S, Lamina T. Guidelines of care for the management of primary cutaneous melanoma. J Am Acad Dermatol. 2019 Jan;80(1):208-250. doi: 10.1016/j.jaad.2018.08.055. Epub 2018 Nov 1. PMID: 30392755. (
  8. Goldberg AD, Blankstein R, Padera RF. Tumors metastatic to the heart. Circulation. 2013 Oct 15;128(16):1790-4. doi: 10.1161/CIRCULATIONAHA.112.000790. PMID: 24126323. (

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!


My patient presents for evaluation of a mole on her arm. What features of the mole should I look for to help me distinguish a benign mole from melanoma?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.