Thin Nevus-Associated Melanoma: Beyond MIA Score Risk Stratification

Area of Science:

• Dermatology
• Oncology
• Pathology

Background:

• Nevus-associated melanomas (NAM) are often diagnosed early, but risk within thin tumors is unclear.
• Classical histopathologic features' role in refining risk for thin NAM needs evaluation.
• Understanding risk factors in thin NAM is crucial for accurate prognosis.

Purpose of the Study:

• To assess the prognostic value of histopathologic features in thin nevus-associated melanoma (pTis-pT1a, <0.8 mm).
• Specifically investigate mitotic activity and tumor-infiltrating lymphocytes (TILs) in thin NAM.
• Determine if these features refine risk stratification for early-stage melanoma.

Main Methods:

• Retrospective cohort study of 138 patients with confirmed NAM.
• Subgroup analysis of 100 patients with thin NAM (pTis-pT1a) for adverse outcomes within 10 years.
• Statistical analysis using chi-squared tests and logistic regression, with AJCC 8th edition staging.

Main Results:

• Among 100 thin NAM patients, 8% experienced adverse outcomes (metastasis or death).
• Higher mitotic activity (≥ 1/mm²) showed a trend towards increased adverse events (10.9% vs. 2.8%).
• Absent TILs were associated with higher adverse event rates (13.8%) compared to brisk TILs (0%).

Conclusions:

• Thin nevus-associated melanomas exhibit risk heterogeneity and are not uniformly low risk.
• Mitotic activity and absent tumor-infiltrating lymphocytes are associated with increased adverse event rates.
• Classical histopathologic features can potentially refine risk stratification for early-stage NAM.