Scalp melanoma: epidemiological, dermatoscopic, histopathological and molecular differences between melanoma located in area covered by hair and melanoma located in exposed area of bald patients

Abstract

Scalp melanomas are usually diagnosed thicker than those in other regions, with a risk of death 2 times greater than tumors located in extremities. The reasons for this worse prognosis are uncertain and discussed in the literature. One of the hypotheses would be that the coverage by the hair would result in a later diagnosis since the initial lesions would be hidden; another hypothesis would be the high proportion of melanomas with rapid vertical growth, such as nodular and desmoplastic, subtypes associated with chronic solar damage. The high blood and lymphatic flow and the difficulty to obtain adequate margins are other hypotheses discussed in the literature. The key point for the favorable prognosis of melanoma is an early diagnosis, with subsequent surgical excision. Dermoscopy increases the diagnostic accuracy of melanoma by up to 30% compared to the naked eye. The dermatoscopic patterns of melanoma are affected by the anatomical location and pattern of sun exposure. Despite advances in understanding the dermatoscopic features of melanoma on the face and trunk, little is described the dermatoscopic pattern of melanoma on the scalp. It is recognized that melanoma is the most frequently mutated cancer, with mutations predominantly caused by the mutagenic effect of ultraviolet (UV) radiation. There is growing evidence that different types of mutations determine the morphology and biology of melanoma. Melanoma of the scalp affects especially bald patients, and baldness provides greater exposure of the scalp to the sun's rays. Melanomas located on the skin with chronic solar damage have a lower frequency of mutations in the BRAF gene, whereas mutations in the NF1, KIT, and NRAS genes are more observed. Although the classification of melanoma into molecular subtypes is constantly expanding and is revolutionizing the treatment of advanced disease, the profile of mutations associated with this neoplasia in the scalp has not been investigated and could elucidate the peculiar behavior of this tumor and optimize the treatment. Objectives: To characterize the mutational profile in BRAF, KIT, NF1 and NRAS genes in melanoma located in the scalp and to associate with the dermatoscopic and anatomopathological characteristics of the tumors. Methods: Retrospective, cross-sectional, observational study of patients with histopathological diagnosis of scalp melanoma between January 2008 and December 2018, at the A.C.Camargo Cancer Center. Tumors with images in the Skin Cancer Nucleus image database will be evaluated for specific dermatoscopic features of melanoma and melanoma on chronic photodamaged skin. For the group of patients with a dermatoscopic image, a histopathological revision will be performed, a search of the mutations in the BRAF, NRAS, KIT, and NF1 genes, quantification of the capillary density and graduation of elastosis at the tumor site. Expected results: 150 patients with melanoma of the scalp and 50 with dermatoscopic images. It is expected to dermatoscopic pattern and mutational profile of melanoma in areas exposed in bald patients similar to that of skin with chronic photodamage; and dermatoscopic pattern and mutational profile of melanoma in hair-covered areas similar to that of melanoma intermittently exposed to the sun. Partial results: 124 patients: 95 men and 29 women, mean age 61.9 years, extensive superficial histological subtype in 60.5% of cases, mean Breslow thickness 2.57 mm. 36 patients with dermatoscopic image: 61.1% tumor in the area covered by hair and 38.9% tumor exposed in the area of baldness. Baldness was associated with males (p = 0.013); advanced age (p <0.001); specific dermatoscopic criteria for melanoma on skin with chronic sun damage (p <0.001); personal history of non-melanoma skin cancer (p = 0.03). The mean Breslow thickness was 1.35 mm for melanomas in covered areas and 0.62 mm for those of exposed areas (p = 0.2). (AU)