Melanocytic nevi are benign tumors of melanocytes; these growths include common acquired melanocytic nevi and other benign melanocytic neoplasms, such as blue nevus, halo nevus, congenital nevomelanocytic nevus, “dysplastic” melanocytic nevus, and Spitz nevus (1–3). Common acquired melanocytic nevi are the most frequent neoplasms. It is unnecessary to remove melanocytic nevi routinely, but they should be removed when any of the following conditions are met: changes in skin lesions, an atypical clinical appearance suspicious for melanoma, cosmetic requirements, or repeated stimulation (4).

In fact, studies have found that common acquired melanocytic nevi are challenging to differentiate in clinical practice from other benign melanocytic neoplasms, such as congenital nevomelanocytic nevus and blue nevus, or even tumors, such as melanoma (5). Moreover, the importance of melanocytic nevi is related to melanoma. A large proportion of melanoma occur in the same area as long-term pre-existing melanocytic nevi (1). Histological examination has shown that approximately 30% of melanoma cases are associated with a residual nevus (6). Therefore, to provide support for clinicians in diagnosing and treating melanocytic nevi, our study focuses on patients with a clinical diagnosis of melanocytic nevi, which are reclassified after a histopathological examination, and assesses whether the clinical characteristics of patients affect the misclassification.

This is a retrospective review of data from 4,561 consecutive patients with a clinical diagnosis of melanocytic nevi over 5 years, from 2014 to 2019, referred to the Department of Dermatology of Xiangya Hospital, Central South University. All patients in this study had undergone an initial clinical diagnosis, excision, and histopathological diagnosis. The reasons for removal of melanocytic nevi included atypical clinical features, changes in skin lesions, cosmetic requirements, or repeated stimulation (e.g., sites of friction or repeated trauma) (4). To ensure accuracy, two independent dermatopathologists reviewed the hematoxylin-and-eosin-stained slides and made a diagnosis. If there is any disagreement among them, another dermatopathologist reviewed the slide, and the three dermatopathologists made the diagnosis together. Clinical data on each case, including the age and sex of the patient and the location of the lesion, were obtained from the patient records. This study was approved by the ethics committees of Xiangya Hospital of Central South University, Changsha, Hunan, China, and informed consent was obtained from all subjects.

The diagnosis and the classification of skin lesions were performed according to Fourth Edition Dermatology (edited by Bolognia, J. L.) (7). Histopathological concordance, which means the consistency of clinical and histopathological diagnoses, was assessed for neoplasms clinically diagnosed as melanocytic nevi and histopathologically diagnosed as common acquired melanocytic nevi or other benign melanocytic neoplasms, such as congenital nevomelanocytic nevus, blue nevus, lentigo, “dysplastic” melanocytic nevus, recurrent nevus, Spitz nevus, and halo nevus. Histopathological discordance, which means the inconsistency between clinical and histopathological diagnoses, included clinical diagnosis as melanocytic nevi and histopathological diagnosis as seborrheic keratosis, basal cell carcinoma, vascular tumor, fibroma, epidermoid cyst, wart, melanoma, Bowen's disease, squamous cell carcinoma, keratoacanthoma, and other neoplasms.

The records of 4,561 patients were reviewed to assess demographic and clinical factors, reasons for removal, and histopathological diagnosis. We first compared the clinical diagnosis with the histopathological diagnosis to establish a histopathological concordance rate and then investigated the effect of clinical characteristics and the reasons for removal on misclassification. Statistical analysis was performed using a χ² test and Fisher's exact test. A two-tailed P < 0.05 was considered statistically significant. All statistical analyses were performed using the SPSS 23.0 statistical package (IBM SPSS, Chicago, IL, USA).

Melanocytic nevi are the most common benign neoplasms of the skin and are also the most easily misdiagnosed skin disease (5). Our study collected excised lesions clinically diagnosed as melanocytic nevi in a Chinese population over 5 consecutive years. The results showed that the consistency of the clinical and histopathological diagnoses of melanocytic nevi was 82.11% after the histopathological examination. Among them, 90.25% were common acquired melanocytic nevi, and 9.75% were other benign melanocytic neoplasms, such as congenital nevomelanocytic nevi, blue nevi, and lentigo. More importantly, 17.89% of patients were reclassified as having other diseases after the histopathological examination. The most common diagnostic change was to seborrheic keratosis, followed by basal cell carcinoma. Overall, 24 (0.53%) patients were reclassified as having melanoma. In addition, clinical characteristics, such as sex, age, and location of the lesion, and the reasons for removal have a potential impact on misclassification.

Morphologically, common acquired melanocytic nevi are challenging to distinguish from other benign melanocytic neoplasms (8). Our study found that, among the cases with histopathological concordance, 9.75% were other types of benign melanocytic neoplasms. In addition, the results showed that younger age was significantly associated with the histopathological diagnosis of congenital nevomelanocytic nevus and Spitz nevus, compared with common acquired melanocytic nevi. The reason for the clinical significance of congenital nevomelanocytic nevus (CMN) is the risk of malignancy (9). The malignancy potential of CMN is well-characterized in congenital melanocytic giant nevi (10). However, the possibility of melanoma development has also been clearly verified for medium and small nevi (11). Spitz nevus is predominantly observed in children and adolescents. In children, a Spitz nevus presents as isolated, domed nodules with a smooth surface and a bright red to brown color. In adults, a Spitz nevus is usually dark in color with brown to black papules, nodules, and nodes (12–14). Because of the difficulty of the clinical diagnosis of Spitz nevus, histopathological examination is necessary (15, 16). Therefore, patients should be asked for a detailed medical history, and lesions in younger patients should be differentiated from congenital nevomelanocytic nevus and Spitz nevus. “Dysplastic” melanocytic nevus, also known as atypical melanocytic nevus, is unusually large and variable in form and shows atypical asymmetry, size, borders, and coloration (7). Moreover, “dysplastic” melanocytic nevus is challenging to distinguish from common acquired melanocytic nevi and melanoma (17). Importantly, it has been reported that melanoma can develop in “dysplastic” melanocytic nevi with a probability of 1:200 to 1:500 and that the presence of several “dysplastic” melanocytic nevi increases the melanoma risk (3). Our data found that the percentage of “dysplastic” melanocytic nevus lesions occurring on the lower limbs was higher than that in patients with a histopathological diagnosis of common acquired melanocytic nevi. Therefore, lesions on the lower limbs with atypical clinical features should be given a detailed physical examination and carefully differentiated from common acquired melanocytic nevi.

In this study, 17.89% of lesions were reclassified as other diseases after the histopathological examination. The most common diagnostic change was seborrheic keratosis, a common benign epidermal tumor (18). Seborrheic keratosis is generally a roundish, scaly, reddish to brownish lesion; it is most common in individuals over 50 years old (19, 20). Clinically, seborrheic keratosis can mimic the appearance of melanocytic tumors (21). Our study found that male sex, older age, and location of the lesions on the trunk and limbs have a potential impact on the misclassification of seborrheic keratosis. Thus, skin lesions with the above-mentioned characteristics should be differentiated from seborrheic keratosis. More importantly, after the histopathological examination, 1.89% of patients were reclassified as having non-melanoma skin cancer (NMSC), including 64 with basal cell carcinoma, 16 with Bowen's disease, four with squamous cell carcinoma, and two with keratoacanthoma. NMSC is the most common human cancer, and sun exposure is an important risk factor for this disease (22). In addition, it has been reported that the incidence of NMSC is higher in men than in women, and 80% of cases occur in people aged 60 years and older (23). Basal cell carcinomas are usually small and have a translucent or pearly appearance (24, 25). Approximately 80% of all basal cell carcinomas occur on the head and neck. Unlike basal cell carcinomas, squamous cell carcinomas can have precursor lesions, such as actinic keratosis and Bowen's disease (26), and typically develop on sun-exposed sites. These studies support our findings. Our study found that male sex was significantly associated with changes in diagnosis to basal cell carcinoma and Bowen's disease. Old age and sun-exposed sites (head and neck) have a potential impact on the misclassification of NMSC, except for Bowen's disease. Lesions on the perineum and buttocks were significantly related to a change in diagnosis to Bowen's disease. Therefore, melanocytic nevi-like lesions in elderly and/or male patients and on sun-exposed skin should be carefully differentiated from basal cell carcinoma and squamous cell carcinoma, and lesions on the perineum and buttocks should be differentiated from Bowen's disease.

The most important task in the diagnosis of melanocytic nevi is to differentiate these lesions from melanoma. We found that 24 patients were reclassified as having melanoma after the histopathological examination. Sex had no effect on misclassification. However, older age and lesions on the hands and feet were significantly related to a change in diagnosis to melanoma, which might be related to the characteristics of melanoma in China. The incidence of cutaneous melanoma is rising faster than that of any other solid tumor (27, 28). Superficial spreading melanoma is the most common type of cutaneous melanoma in Caucasians (29). However, acral melanoma is a common subtype of melanoma in Chinese patients, while it is rare in Caucasian patients (30–33). Melanoma can develop from pre-existing nevi in approximately 20–40% of cases (34). Early diagnosis is the key to improving the survival rate (35). The ABCDE rules (asymmetry, border irregularity, color variegation, diameter, and evolution) are useful for the early identification of melanoma (36). In addition, dermatoscopy improves diagnostic accuracy, particularly in the differential diagnosis between benign and malignant melanocytic tumors. Furthermore, the results showed that, in addition to atypical clinical features, the percentage of lesions removed due to lesion changes and repeated stimulation was significantly higher in lesions whose diagnosis was changed to melanoma than in lesions with histopathological concordance. Therefore, our study shows that melanocytic nevi should be differentiated from melanoma in elderly patients when the lesions are in load-bearing and friction-prone sites or in the event of changes or repeated stimulation.

In summary, our data demonstrate that histopathological review results in a change in diagnosis in 17.89% of patients with the clinical diagnosis of melanocytic nevi. In addition, clinical characteristics have a potential impact on misclassification. In addition to atypical clinical manifestations, lesions in elderly patients, lesions in sun-exposed, load-bearing, or friction-prone locations, and lesions with changes or repeated stimulation should raise the clinical suspect and be carefully differentiated from malignant tumors.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

The studies involving human participants were reviewed and approved by the ethics committees of Xiangya hospital of Central South University, Changsha, Hunan, China. Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

PL performed the study design, data analysis, and manuscript writing. XZ, MC, XC, JL, and CP contributed to data collection and validation. YK, MC, and XC performed the clinical diagnosis and samples collection. JS, YK, and WZ were clinical experts and performed the manuscript revision. All authors read and approved the final version of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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