Sir,

Malignant blue nevus is a rare form of melanoma that usually arises from a pre-existing blue nevus. Diagnosis can be challenging, and is based on patient history, clinical manifestations and histopathology. We report a case of Malignant blue nevus in a young patient.

A 17-year-old female patient, who had a history of two blue nevi on her buttocks since early childhood, presented a recent enlargement of one of these lesions with secondary ulceration.

Clinical examination revealed Fitzpatrick Skin Phototype IV and two lesions of the left buttock. The nodular lesion was oval-shaped, bluish, and had well-defined borders. It had a lower ulceration covered in a crust, measured 2 cm by 1.5 cm, and was located on the superior internal quadrant (Fig. 1). The papular lesion was symmetrical, blue, and measured 3 mm in the superior external quadrant.

Figure 1: Clinical presentation of Malignant Blue Naevus; a blue nodule of 2cm/ 1.5cm, with inferior ulceration, located on the left buttock.

Dermoscopy of the nodule (Dermlite DL4,*10, polarized light) showed a heterochromic lesion consisting of black and blue, a blue gray veil, and an asymmetrical ulceration of 3 mm (Fig. 2). The papule had well-defined borders and a structureless blue pattern.

Figure 2: Dermoscopic features of Malignant Blue Nevus (Dermlite DL4,*10, polarized light); heterochromic nodule; consisting of black and blue, areas of shiny white structures and ulceration.

A skin biopsy of the nodule showed infiltrating melanocyte proliferation, reaching the reticular dermis, associated with multiple mitoses and cellular atypia. Systemic assessment that included cerebral and thoraco-abdomino-pelvic tomography showed unilateral inguinal lymphadenopathy without distant metastasis.

Therapeutic management consisted of an excision with margins of two centimeters and unilateral lymph node dissection. Histological examination concluded to an infiltrating melanoma, Clark at V and Breslow at 6 mm without nervous infiltration. Nodes were negative, and no intraepithelial component was found (Figs. 3a and 3b). The stage was pT4bN0M0, according to the 8^th edition of the AJCC. It also showed a blue nevus component on the periphery, made of ovoid and spindle-shaped proliferation without cytonuclear atypia or abnormal mitosis. Hence, the diagnosis of malignant blue nevus was made. Clinical monitoring for 3 years found no evidence of relapse.

Figure 3: a and b Histopathology (HEx 20) of Malignant Blue nevus; compact clusters of atypical naevic cells infiltrating the dermis and hypodermis, surrounded by histyocytes cells.

Melanoma is an aggressive skin cancer caused by genetic mutations in melanocytes, which account for approximately 1% of all malignant skin tumors [1].

The usual clinical presentation of blue nevi is small macules or dome-shaped papules, measuring about 1-5 mm in diameter, and dark blue or blue-black. Dermoscopy shows a homogeneous pattern with structureless pigmentation, often described as steel-blue coloration [2]. Our patient presented atypical dermoscopical signs; consisting of heterochromia (blue and black), a blue-gray veil, and ulceration.

Histological examination is characterized by dermal melanocytes that appear as melanin-containing fibroblast-like cells, usually grouped in irregular bundles admixed with melanin-containing macrophages and associated with excessive fibrous tissue in the reticular dermis [2].

Malignant blue nevus (MBN) or Blue Nevus Melanoma is a rare and heterogeneous group of melanomas that either arises in association with common or cellular blue nevi or develops de novo but mimics cellular blue nevi on architectural and/or cytological signs [3]. The most predominant anatomic locations were the head and neck region (50%), the boot (21%), and the buttock/sacrococcygeum (17%) [3]. In our case, the patient had the least common location that is the buttock.

Histologic characteristics of MBN include severe atypical cytologic features indicating malignancy, such as pleomorphic (in size, shape, and staining) nuclei, large eosinophilic nucleoli, brisk, mitotic activity, or atypical mitotic figures [4].

There are many controversies concerning this said group. First, it’s challenging differentiating between an atypical cellular blue nevus and malignant blue nevus, as they may express similar clinical and histological features [5] and this type of nevus might even colonize local lymph nodes [6]. Second of all; since there is no epidermal component, usual clinical and pathologic indicators such as Breslow thickness, age, Clark level might not be predictive of outcome to this group of melanomas. Additionally, in term of prognosis, reports found a significant association between the largest and thickness tumors with both recurrence-free survival and reduced time to distant metastasis [3].

Even if malignant blue nevi may not generally behave as aggressively as nodular malignant melanoma, they can produce generalized metastasis and fatal outcome. Therefore, they have to be removed by wide surgical excision with a specific following up of patients for at least 5 years [7].

Malignant blue nevus remains is a rare and challenging diagnosis both on clinical and histological level. Each dermatologist should be aware of such risk and suspect it in case of recent growth of an old blue nevus, ulceration or any color change. Dermoscopy is usueful in showing atypical patterns of blue nevi, which might help early diagnosis.