Melanoma acral plantar: aspectos epidemiológicos, clínicos, dermatoscópicos e histopatológicos

Abstract

Acral melanoma is a rare subtype of melanoma in which more than two-thirds are located on the plantar surface of the feet. Plantar melanomas represent less than 5% of the total melanomas in caucasians, however they are responsible for more than a third of the tumors in Asians and are estimated as more than 50% of the tumors in African descent populations. Pathogenesis, risk factors and genetic characteristics are still controversial. Chronic trauma has been suggested by several authors to have a role in plantar tumor genesis, while others refute this. Early diagnosis is essential to improve prognosis, but it is challenging, due to its anatomical characteristics, being an underexamined site and by the presence of atypical clinical variants, such as amelanotic tumors. Dermoscopy improves the diagnosis of acral melanomas when the parallel ridge pattern is present, while the parallel furrow pattern is more frequent in plantar melanocytic nevi. Most of the available data regarding epidemiology, clinical features, dermoscopy and histopathology of plantar acral melanoma are from Asian, European and North American populations. Latin American and national data on this matter are scarce. This is a retrospective, observational and analytical study, developed at the Dermatology Clinic of Hospital das Clínicas at UFMG, in which we evaluated the epidemiological, clinical features, dermoscopic and histopathological characteristics of plantar acral melanomas. The sample was chosen by convenience, in a time period from 2005 to 2020. 71 cases were identified, 48 were included for analysis and 36 had photographic documentation. The remaining 12 cases were admitted after of the primary lesion was removed and were included only for epidemiological, clinical (location) and histopathological analysis. Age, sex, occupation, phenotype, clinical features (location, size, delimitation), dermoscopy (patterns, structures and colors) and histopathological characteristics (Breslow thickness, presence of ulceration and mitotic rate), were analyzed for their associations. We found a median age of 62.54 years and a predominance of females (62.5%). There was significant tendency for tumors to be located in the calcaneus (p=0.076) area, which can be demonstrated on the heat map. There was a significant association between delimitation and support, with supporting areas having a higher frequency of imprecise limits and areas without support, a higher frequency of precise limits (p=0.002). The parallel ridges pattern, considered the most specific for diagnosing acral plantar melanoma, had a prevalence of 77.8% [CI95% 61% and 90%]. Polychromy was the most prevalent finding (94.4%). Breslow thickness had a median of 3.84 mm (±3.11) in invasive lesions. The presence of ulceration, identified by histopathology (p 0.013) or dermoscopy (p 0.047), was associated with a higher Breslow thickness. Limitations of this study includes its retrospective and unicentric nature, such as information bias. Despite this fact, to our knowledge this is the first study corelating poor delimitation to chronic trauma. It also contributes to the description of different dermoscopic findings prevalences in acral melanomas on the Brazilian population.