Public enemy No. 1: Melanoma incognito cunningly mimics benign lesion

September 1, 2008

A thorough dermoscopic evaluation of each and every skin tumor in patients can prove invaluable in accurately diagnosing dangerous skin tumors such as melanoma incognito. One expert applies seven "golden rules" to help better manage patients with skin tumors, and to home in on which lesions should be biopsied and which should not.

Key Points

International report - Melanoma incognito has significant potential to pose a great threat to the patient affected, as this malignant skin lesion can cunningly mimic a benign lesion, such as a harmless hemangioma or a common intra-dermal nevus.

According to one expert, such lesions can be very precarious for the patient if an unwary dermatologist does not take extreme care in reaching the correct diagnosis in time.

"In the daily routine, a clinician will perform a skin lesion screening and have a very good idea which lesions are benign and which ones are malignant, or at least suspicious, and those lesions that seem suspicious are rightfully and promptly excised.

With the advent of dermoscopy, dermatologists now have a powerful tool with an ever-increasing list of specific criteria to better evaluate and timely recognize difficult-to-diagnose melanomas.

In order to avoid any bad surprises and to better screen the skin lesions of patients, Dr. Argenziano and colleagues created the "seven golden rules" to help clinicians decide whether a suspicious lesion should be removed:

1. Don't use dermoscopy solely for suggestive skin lesions.

2. Biopsy lesions missing clinical-dermoscopic correlation.

3. Biopsy lesions with unspecific pigment pattern.

4. Biopsy lesions with spitzoid features.

5. Biopsy lesions with extensive regression features.

6. In patients with multiple nevi, biopsy lesions that exhibit change after a short-term follow-up.

7. Biopsy pink lesions with an atypical vascular pattern.

"Over the years, we have seen many clinical cases in which we did not even think about melanoma as being the potential diagnosis because of the benign features they exhibited upon initial clinical examination.

"However, when we used dermoscopy, we realized that (there was) something more to these lesions than first assumed," Dr. Argenziano tells Dermatology Times.

Dr. Argenziano says he first clinically examines a given lesion and decides on a preliminary diagnosis, macroscopically, and then he applies dermoscopy and makes a definitive diagnosis.

In the great majority of cases, the preliminary and final diagnoses agree.

"However, there are those cases where, at first, I think the lesion is benign macroscopically, but upon dermoscopic evaluation, I begin to have my doubts because of the suspicious characteristics seen in the dermoscope," Dr. Argenziano says.

According to Dr. Argenziano, opponents of dermoscopy argue that the technique does not add relevant information that could improve the clinical management of pigmented skin lesions because all clinically suggestive lesions should be biopsied anyway.

He says the dermoscopic evaluation is an invaluable assessment tool in uncovering a rogue skin lesion. When doubt increases after the dermoscopic evaluation, it is time for an excisional biopsy.

Dr. Argenziano says the most important rule for not missing melanoma is to use dermoscopy for each individual lesion in a particular patient. In the past, dermoscopy was considered a kind of second-level procedure, meaning only clinical examinations were performed, and dermoscopy was employed only if a lesion appeared to be clinically atypical.

"Now, we know very well that we have to examine and carefully scrutinize every single lesion that the patient presents with, because clinically, melanoma can very often present as a nonsuspicious lesion; namely, melanoma incognito," Dr. Argenziano says.

According to Dr. Argenziano, the exact magnitude of melanoma incognito is completely unknown in the literature; however, experts believe that melanoma incognito occurs in approximately 5 percent to 10 percent of all histologically proven melanomas.

"The 'truly missed' melanoma is the one that dermatologists send home, as it appeared absolutely benign upon first inspection.

"This is why you will never know if the lesion was a melanoma or not, unless the patient returns for a follow-up examination in which the melanoma may show its true face," Dr. Argenziano says.