Cutaneous Malignant Melanoma Diagnosed on Nonvisible Body Sites and the Importance of Total Body Examination: a Retrospective Cohort Study

The incidence of cutaneous malignant melanoma (MM) is increasing worldwide. Regular self-skin examination can assist in the early detection of MM. However, identifying new or changing lesions on nonvisible body sites (NVBS) can be difficult. Research investigating MM on NVBS is limited. The aim of this study was to compare the features of MM on NVBS with visible body sites (VBS) to add data to this patient cohort. We performed a retrospective chart review to identify patients diagnosed with MM in our institution from 2019 to 2021. Clinicopathological features were extracted and analysed. NVBS was defined as areas including the posterior scalp, ears and neck, posterior shoulder, back, buttocks, posterior thigh and plantar aspect of the feet. Statistical analysis was performed using SPSS (IBM). A total of 162 patients were included in this study; 45.1% (n = 73) were male. Patients with MM on NVBS were statistically significantly younger (median age 59 years) compared with patients with MM on VBS (median age 66.5 years; P < 0.05). Thirty-seven per cent (n = 60) of lesions were found on NVBS. Twenty-eight per cent (n = 17) of MMs on NVBS were identified incidentally on total body examination (TBE) in the clinic by a dermatologist. There was a statistically significantly higher number of patients with melanoma in situ on VBS (n = 44; 27.1%) compared with NVBS [n = 17; 10.5% (P < 0.01)]. A higher proportion of patients with MM on NVBS had a Breslow thickness > 1 mm (n = 23; 38.3%) vs. VBS (n = 30; 29.4%). This study demonstrates a higher number of MM diagnosed incidentally following TBE compared with previous research. Our study focused on a MM-specific cohort who may, potentially, have had lethal skin cancers missed in 28% of cases if TBE was not carried out. Our findings also show that patients are more likely to have noninvasive tumours detected on VBS but more advanced disease on NVBS, further emphasizing the importance of TBE. This study suggests that high-risk patients could benefit from specific surveillance programmes that encourage regular self-skin examination and periodic TBE by a consultant dermatologist to enable early detection and treatment of MM. This study was limited by its retrospective design and a small number of patients from a single institution. We recommend an increased emphasis on patient education on the importance of self-examination which, when complemented by physician-directed TBE, plays a valuable role in the early detection of MM on NVBS. This study provides guidance in designing pathways to target high-risk groups to avoid delays in the diagnosis of MM. Further research to explore trends of MM on NVBS may enable targeted education campaigns in the future.