Nodular malignant melanoma in vulvar skin without pigmentation: a case report - BMC Women's Health - BMC Blogs Network

Melanoma is a highly aggressive cutaneous malignancy with considerable risk for metastasis. In dermatologic and diagnostic pathology, we divide melanomas into 4 subtypes based on the different characteristics of their histopathology, including diffuse surface, nodular, freckled, and terminal pigmented melanomas. These malignant tumors are typically pigmented given that they arise from melanocytes, who can produce melanin. Considering the disease's metastasis and related mortality mainly depends on the thickness of the tumor and the depth of invasion, thus early detection and correct diagnosis are important to improve the prognosis of patients with melanoma. However, it is difficult to make an accurate diagnosis for melanoma at early stage in China [10].

In our present case, this patient had large polyps on her vulvar skin, but she did not look for help from professionals. Until nearly a month, she found that the lesion was prone to bleed after friction, so she came to our hospital for treatment.

According to the literature, it is reported that nodular melanoma generally has the following characteristics under dermatoscopy: peripheral black dots/globules, multiple brown dots, irregular black dots/globules, blue-white veil, homogeneous blue pigmentation, 5 to 6 colors, and black color, for instance, it was reported as milky red with homogeneous red structure; shiny white structure (crystalline structure); various pink colors; and irregular linear blood vessels [11].

It is well documented that NM often lacks pigmentation [12], which indicates that the diagnosis of NM cannot rely on the pigmentation in the tissue but vascular morphology [13]. The dermatoscopic findings indicated that the milky-red areas, short white shiny streaks (only seen under polarized dermoscopy) and polymorphic vascular morphology were the only clues for the diagnosis [12, 13]. The most common combination of blood vessel types in melanoma is linear, coiled, and spotted. Although short, shiny white streaks are not very specific for the diagnosis of NM, they are rarely seen in benign skin tumors, therefore, representing an important standard for NM treatment.

Back to our case, dermatoscopic images showed there was a dark-red background with short white shiny streaks, and the vessel types were linear, coiled, and spotted. Although no typical dermatoscopic changes were found, we tended to diagnose the lesion as a type of skin tumor.

Further performances such as histopathological analysis and IHC on the skin lesions of this patient were conducted. A variety of IHC staining biomarkers are widely accepted for the diagnosis of melanoma, including S-100, HMB-45 and Melan-A. S-100 is reported to be the most sensitive marker. Besides, specific HMB-45, S-100 and Melan-A are close to 100 %, 75–87 % and 95–100 %, respectively [14]. IHC analysis of this patient showed a strong positive of S-100 tumor cells protein, additionally, Melan A and HMB45 were all positive. Therefore, this case was confirmed as malignant melanoma nevus and nodular malignant melanoma formation.

Although NM accounts for 14–15 % of all CM patients, there are several different points between them, such as prognosis, mutational profile, and histopathologic characteristics. A previous clinic trial analyzed [15] 350 patients with vulvar melanoma from 6436 vulvar cases in the Dutch Cancer Registry between 1989 and 2012, the results of prognosis showed that the 5-year OS of women with vulvar melanoma was 35 % (95 % CI 26.7–44.4 %), compared to 50 % (95 % C=: 40.5–59.1 %) for matched-CM patients (p = 0.002). The prognostic factors of vulvar melanoma are mainly affected by Breslow's thickness, AJCC tumor stage and lymph nodal status [16, 17]. In addition, the literature about mutational profiles of vulvar melanoma and CM demonstrated that BRAF mutations are most common (50 − 60 %) in CM, while c-KIT and NRAS mutations (27.6 %) commonly exist in vulvar melanoma [18]. The histologic features include atypical melanocytes, which mostly distributed in the basal layers. The invasive atypical melanocytes mainly distributed in nests, which could be epithelioid, spindle and other forms. Melanin pigment can be diffuse or focal and even absent. In China, polypoid nodular malignant melanoma on the vulvar skin is rare, and there is no accurate and practical diagnostic standard for this disease in the clinic. Hence, it is crucial to make the right diagnosis at the early stage of melanoma using dermoscopy or other approaches, performing histopathology and immunological examinations in time, and conducting the early detection and treatment to help these patients improve their prognosis.

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