César Bimbi¹; Amanda Nichele²; Jubin Yoo²; Uwe Wollina^{3, 4}

¹ Private Clinic, Dermatologia Medica & Laser, Porto Alegre, Rio Grande do Sul, Brazil.

² Medical Student at Universidade do Vale do Rio dos Sinos, São Leopoldo, Brazil.

³ Former Head of Department of Dermatology & Allergology, Städtisches Klinikum Dresden, Academic Teaching Hospital, Dresden, Germany.

⁴ Adjuvant International Adjuvant Faculty, Department of Dermatology, Venerology & Leprosy, Jawaharlal Nehru Medical College, Datta Meghe Institute of Higher Education & Research – Premier Deemed to be University, Wardha, Maharashtra, India

Introduction

In recent decades, increasing incidence rates have reclassified malignant melanoma (MM) from a rare disease to a cancer of growing importance. Among its subtypes, cutaneous amelanotic melanoma (AM) is a rare and aggressive form, representing about 1 to 8% of all MM cases. Due to the lack of pigmentation, its appearance can vary, often mimicking benign conditions such as cysts or less severe malignant conditions like basal cell carcinomas with pink skin coloration. This often leads to delayed diagnosis of AM, which can result in treatment delay and consequently an unfavorable prognosis [1].

The case of the patient presented here is illustrative as the clinical presentation of melanoma was initially considered as an inflamed or ruptured epidermal cyst, a more prevalent lesion. An epidermal cyst is a well-encapsulated benign lesion that often contains keratin in the stratified squamous epithelial walls [3]. By sharing this case, the importance of a thorough dermatological evaluation in the presence of any suspicion of malignant skin lesion is emphasized. This approach aims to prevent delays in diagnosis and ensure timely treatment, contributing to improving the prognosis and quality of life of affected patients.

Case Report

An 86-year-old female patient with a history of basal cell carcinoma sought medical attention in 2021 complaining of a nodular lesion on the right forearm. At this initial visit, she was diagnosed with an epidermal cyst, and due to a comorbid cardiac condition, there was a lack of consensus regarding surgical excision. As the lesion continued to increase in size, the patient sought dermatological care in July 2023. She denied itching, pain, or other associated symptoms. Dermatological examination revealed a violaceous plaque with an ulcerated nodular center, measuring 6.0 x 5.0 cm, on the proximal extensor site of her right forearm.

Fig. 1

An excisional biopsy was performed, revealing a nodular amelanotic malignant melanoma, with a Breslow depth of invasion of 47.0 mm, in a vertical growth phase, Clark level V infiltration, and presence of 15 mitoses/mm². There was no identification of regression or satellitosis. Ulceration was present, while angiolymphatic and perineural invasion were not identified. Urgent surgical removal with safety margins was recommended, as well as systemic evaluation for metastases. Radial and deep surgical excision was performed with a safety margin of 20.0 millimeters radially and 0.3 millimeters in the depth. The pathological staging revealed a pT4b stage. The prognosis is unfavorable due to cancer progression.

Discussion

The well-known and useful ABCDE rule (asymmetry, irregular border, color variation, diameter greater than 6 mm, and evolution) is valuable for differentiating concerning melanomas and atypical nevi from benign pigmented lesions. However, the presented AM variant deviates from this rule, highlighting the complexity and importance of detailed clinical surveillance for early and accurate diagnosis of these skin lesions [2-5].

There are three main clinical forms of AM: (a) erythematous macule with epidermal changes due to sun exposure, (b) dermal plaque with skin-like coloration, without changes in the epidermis, and (c) papulonodular form. The papulonodular form accounts for more than half of AM cases and can manifest as an ulcerated nodule or a “vascular” lesion, often mimicking other conditions such as pyogenic granuloma, hemangioma, or even an inflamed or ruptured epidermal cyst, as in the case of the present patient. Other non-papulonodular forms of AM may mimic eczema or colored dermal plaques and rarely exhibit the ‚ABCDE‘ criteria that typically aid in the diagnosis and screening of melanomas. There is an absence of melanin, and AMs may appear normochromic or erythematous [1, 6, 7].

Patients with characteristics such as red hair, Fitzpatrick skin type I, presence of freckles, sun-sensitive phenotype, or previous history of MM are more predisposed to develop AMs. It is important to note that any subtype of melanoma can be amelanotic. Additionally, these cases tend to present characteristics such as greater Breslow thickness, high mitotic rate, more frequent ulceration, more advanced tumor stage, and lower survival rate compared to pigmented melanoma [6]. AM shows some characteristic point mutations (Table 1) [8].

At the consultation one year ago, the patient had a smaller lesion, contributing to confusion with an epidermal cyst. The delay in diagnosis compromised the patient’s prognosis, as the average survival after MM diagnosis at pT4b staging is only a few months. Dermoscopy, is of limited value for diagnosis and follow-up in AM patients [9].

The discussion of this case reinforces the importance of meticulous evaluation of suspicious lesions, along with histopathological examination, even in cases that may initially appear benign.

Funding:

There was no funding.

Conflict of interest:

There is no conflict of interest.