Amelanotic Lentigo Maligna Melanoma

Alejandra M. Abeldaño, MD; María Emilia Saadi, MD; Pablo Brea, MD; María Cristina Kien, MD; Edgardo Chouela, MD

Disclosures

Skinmed. 2004;3(1) 

A 72-year-old woman presented with a slightly erythematous macular lesion measuring 333 cm, with undefined borders, on the left temporal area of the face. The patient could not state how long ago she had noticed the lesion or whether it had grown gradually. There was no significant adenopathy and the remaining physical examination findings were unremarkable. A complete blood examination was within normal parameters (Figure 1).

72-year-old woman with a slightly erythematous macular lesion on the left temporal area of the face.

The lesion was considered to be clinically suspicious for actinic keratosis, Bowen's disease, and discoid lupus erythematosus, and a punch biopsy specimen was obtained. Histologic examination showed proliferation of atypical melanocytes devoid of melanin pigment, some of them spindle-shaped, infiltrating the papillary dermis. A moderate lymphocytic infiltrate and solar elastosis were present. The patient was diagnosed with lentiginous maligna melanoma with Clark's level not less than II and Breslow's thickness not less than 0.49 mm (Figures 2 & 3). The histologic features were those of amelanotic lentigo maligna melanoma. A wide excision was recommended.

Proliferation of atypical melanocytes involving epidermis and adnexal epithelium and infiltrating dermis (hematoxylin-eosin stain, 100x).

Large atypical melanocytes in the epidermis and dermis (hematoxylin-eosin stain, 400x).

Amelanotic melanoma represents 1.8%-8.1% of all such melanoms. Any clinical subtype of cutaneous melanoma may be amelanotic, although it is more common of subungual tumors (25%) and desmoplastic melanoma (more than 50%). Therefore amelanotic lentigo maligna melanoma (ALMM) is even more rare.[1] Since the first reported case[2] of ALMM as an "unpigmentierte melanosis praeblastomatosa," 27 cases have been published, including those published in 1957[3] and 1958[4] as extramammary Paget's disease of the scrotum. Based on these cases and those reviewed by others,[5] there is no definite or unique feature that may point to the diagnosis. A review of reported ALMM cases is shown in Table 1 .

According to a review of the literature, typical patients are elderly women (ratio 3:1) and the average age is 61.8 years. The most common localizations are the face -- especially the cheek and temple area, as in our reported case -- and upper extremities.

ALMM's clinical presentation has no specific features and most cases are misdiagnosed. The most common misdiagnoses are listed in Table 1 . ALMM usually presents as a nonpigmented, erythematous macule, sometimes with a slightly scaled surface and irregular, indistinct borders. Occasionally, it resembles a nonspecific swelling or normal skin-colored nodule. The lesion is almost always asymptomatic.[5,14,15,18]

In the case discussed here, the lesion was suspicious for actinic keratosis, Bowen's disease, and discoid lupus erythematosus. The final diagnosis was achieved by histopathologic examination.

In ALMM the tumor originates at the epidermal-dermal junction where an irregular junctional activity takes place with downward streaming of tumor cells with anaplastic nuclei from the epidermis into the dermis. Lateral intraepidermal extension of melanoma cells beyond the borders of the dermal tumor may lead to disintegration of the epidermis and ulceration. The tumor cells show great variation in size and shape; however, the spindle-shaped type is most frequently seen. Mitoses are usually present, but only in small number. Melanin is absent or small amounts can be found with the Fontana-Masson stain, or, if fresh tissue is available, the dopa reaction can prove positive in at least part of the tumor.[21]

The etiology of the amelanotic component remains unknown. Two hypotheses have been suggested for melanocytes lacking pigment: 1) agenesis of melanosomes; and 2) abnormal melanogenesis. Some authors[5,14,18] believe that it could be related to the absence of the tyrosinase enzyme necessary for melanin synthesis. Others suggest that melanin is produced at low concentrations that go undetected clinically or histopathologically.

The prognosis of ALMM is not different from other melanomas having the same thickness and similar location. Therefore, prognosis is sometimes unfavorable if the correct diagnosis is achieved at a late stage, when the lesion is clinically evident, or when nodules arise, allowing the melanoma to progress to a potentially fatal outcome.[8,17] The potential risk of an in situ lentigo maligna becoming an invasive melanoma is unknown. There are no long-term follow-up studies so the frequency of progression remains uncertain.[17]

The most widely accepted treatment is local excision with a 0.5-2-cm margin depending on the Breslow's thickness. Destructive therapies such as radiotherapy and cryosurgery with liquid nitrogen have shown significant failure rates. They should be considered only for patients in whom surgery is judged to be impractical.[22]

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