Melanoma hyperpigmentation is strongly associated with KIT alterations.

Area of Science:

• Oncology
• Dermatology
• Molecular Biology

Background:

• KIT alterations are implicated in melanoma pathogenesis.
• Imatinib treatment shows some efficacy, but KIT's role in melanoma histology is unclear.
• Understanding KIT's relationship with histological features is crucial for targeted therapy selection.

Purpose of the Study:

• To investigate the association between KIT protein expression and various melanoma histological features.
• To determine the correlation of KIT alterations with clinical and pathological variables.
• To identify histological indicators that may predict KIT aberrations in melanoma.

Main Methods:

• Evaluated KIT protein expression via immunohistochemistry in 70 melanoma cases.
• Analyzed KIT expression against histological variables: subtype, sun damage, tumor-infiltrating lymphocytes, in situ component, vertical growth phase (VGP), location, and hyperpigmentation.
• Performed mutational analyses for KIT exons 9 and 11, and BRAF on cases with high KIT expression.

Main Results:

• High KIT expression (3+ membranous staining) was observed in 28 cases.
• Significant univariate associations included inverse relationships with sun damage and VGP, and correlations with tumor location, subtype, and hyperpigmentation.
• Multivariate analysis identified hyperpigmentation (P = 0.002) and VGP (P = 0.019) as statistically significant predictors of high KIT expression.
• KIT mutations were uncommon (2/27 in exon 11), with only one BRAF V600E mutation found.
• The frequency of KIT aberrations increased to 40% in cases with hyperpigmentation and VGP.

Conclusions:

• KIT aberrations are not limited to acral or mucosal melanomas.
• There is an inverse relationship between KIT abnormalities and sun damage.
• Hyperpigmentation is a strong predictor of KIT aberrations, overriding other histological factors.
• Histological features like hyperpigmentation and VGP can help identify melanomas with potential KIT aberrations for further investigation and targeted therapy.