The role of microsatellite lesions in melanoma

• The AJCC 8^th edition amended the definition of a microsatellite to be a cutaneous or subcutaneous metastasis completely discontinuous from a primary melanoma, with unaffected stroma in the space between.¹
• Microsatellites may have prognostic significance in melanoma, acting as an adverse prognostic feature, and this has been evaluated in a case-control study based on the new definition.²
• The results showed that for overall and disease-free survival, the microsatellite distance was the strongest predictor of adverse outcome, although size was also very high.²
• In the overall cohort, lympho-vascular invasion was the strongest predictor, and there were statistically significance differences in recurrence between patients with and without microsatellites.²
• The presence of microsatellites was the only factor that proved to be an independent predictor of sentinel lymph node positivity after adjustment for other variables in the model.²

Primary cilia as biomarkers

• It has been suggested that the primary cilia could be a biomarker for acral melanoma.³
• This may be useful since there are overlapping histological features between acral melanoma and nevi, but key differences in primary cilia.
• In the acral melanoma, ciliation index has been shown to be 9.3%, compared to 74.0% in nevi.³ This is useful to help distinguish benign lesions from acral melanomas.

miRNAs as biomarkers

• Due to their small size, miRNAs are relatively stable, and can be analyzed even in relatively old specimens. miRNAs have been evaluated in melanoma prognosis, especially those correlating with thickness.⁴
• There was differential expression of 50 miRNAs, and two – miR-146 and miR-21 – were upregulated in thicker melanomas, and correlated with Breslow thickness in superficial spreading melanoma, but not in nodular melanoma.
• For overall survival, the miRNA signature was better at predicting survival than Breslow thickness.