Cutaneous Melanoacanthoma

Excerpt

Cutaneous melanoacanthoma is a benign skin tumor. It was originally described by Bloch in 1927 as a non-nevoid type I melano-epithelioma; subsequently, in 1960, Mishima and Pinkus coined the term melanoacanthoma. The lesion morphology mimics that of melanoma. It typically presents as a solitary black nodule that has been present for nearly 6 years and has increased to a diameter of 2 or more centimeters. It is most commonly located on either the head and neck or the trunk. Microscopic examination shows an epithelial lesion in which the epidermis has a thickening of not only the stratum corneum (hyperkeratosis) but also the other layers (acanthosis); undulation of the epithelium (papillomatosis) may also be present. Importantly, throughout all layers of the entire epidermis, there is a mixture of cell types: melanocytes with large dendritic processes and keratinocytes. The pathogenesis of a melanoacanthoma remains to be established; many researchers consider it to be a variant of seborrheic keratosis. Possible etiologic factors in the development of a melanoacanthoma include secondary colonization of melanocytes, irritation-induced maturation of basal cells into squamous cells that block melanin transfer from the melanocytes into the keratinocytes, and trauma. Visual inspection is the initial evaluation of a patient with a solitary pigmented lesion that is either new-onset or older and increases in growth; typically, a melanoacanthoma is not considered as a diagnostic possibility since the lesion has many clinical, dermatoscopic and reflectance confocal microscopy features that may also be observed in melanoma. The diagnosis is usually established after a biopsy of the lesion has been performed; Fontana Masson stain or an S100 or melan-A—also known as melanoma antigen recognized by T-cells 1 (MART-1)--immunoperoxidase stain can confirm the presence of melanocytes at all levels of the epidermis. Conservative excision of melanoacanthoma is the treatment of choice since incomplete removal of the tumor can result in persistence and continued growth or recurrence of the lesion. It is important for the individuals who provide primary care to patients with new or changing solitary pigmented lesions to refer the patient to a clinician who can evaluate them and perform a biopsy. Management following the biopsy consists of routine wound care and periodic follow-up evaluation to ensure that the melanoacanthoma does not recur.

Melanoacanthoma is a rare benign neoplasm. It can occur in the mouth (or other mucosal epithelium); in this location, it is referred to as an oral melanoacanthoma. In contrast, it can also occur on non-mucosal sites and is designated as a cutaneous melanoacanthoma. This paper focuses on non-mucosal melanoacanthoma; henceforth, unless otherwise specified, melanoacanthoma refers to cutaneous melanoacanthoma.

Benign non-nevoid melanoepithelioma of the skin was described in German by Dr. B. Bloch in the Archives of Dermatology and Syphilology in 1927. He classified the lesion into two types:

1. Type I melanoepithelioma (currently referred to as a melanoacanthoma)

2. Type II melano-epithelioma (now considered to be the pigmented variant of a seborrheic keratosis).

More than 30 years later, in 1960, Mishima and Pinkus presented 13 new cases of benign pigmented skin tumors that were characterized by a proliferation of dendritic melanocytes mixed with hyperplastic epidermal cells (which they described as basal and prickle type Malpighian cells). They considered the lesions to be identical with the type I benign non-nevoid melanoepithelioma that Bloch had described. They also proposed that the tumor be designated as a melanoacanthoma.

After they studied seborrheic keratoses and melanoacanthomas in 1969, the Sanchez Yus and Simon Huarte changed their histologic diagnosis of melanoacanthoma to that of melanocytic seborrheic keratosis. In 1991, they suggested that dermatopathological vocabulary eliminates the term melanoacanthoma. However, neither their proposed nomenclature to replace melanoacanthoma nor their recommendation to abolish the term has not been accepted.

Melanoacanthoma typically presents as a solitary lesion on either the head and neck or the trunk of an elderly individual older than 60 years of age. It is usually a slowly growing black or hyperpigmented cutaneous asymptomatic tumor. The appearance shares many common features with those of a melanoma; therefore, a biopsy is typically done to exclude the possibility of cancer. Once the diagnosis is established, excision is often performed if residual melanoacanthoma is present. Recurrence is rare after the benign tumor has been removed.