C-Kit SCF receptor (CD117) expression and KIT gene mutation in conjunctival pigmented lesions

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Abstract

Purpose

to investigate the presence of KIT gene mutations and immunoreactivity in 85 conjunctival melanocytic tumors and clarify the role of KIT as a potential therapeutic target in this group of patients.

Methods

85 conjunctival pigmented tumors (27 melanomas, 12 PAMs and 46 nevi) were immunostained for KIT. Intensity and pattern of expression were evaluated. Molecular analysis to identify KIT mutations was performed in 15 selected cases (tumor-rich areas >50%). KIT immunostaining score and pattern were statistically related to patients’ age, sex, diagnostic category, presence of relapse, disease-free survival, presence of metastases, metastasis-free survival, limbal versus non-limbal tumor location and thickness of melanomas.

Results

KIT stains was documented in 48% of melanomas, 50% of PAMs and 24% of nevi. The mean score of KIT staining in the melanomas/PAMs group was significantly different from nevi (p=0.0076). No statistically significant differences were detected between either c-kit immunostaining score or pattern and each of the other clinico-pathologic parameters considered. No KIT gene mutations were detected in melanomas and nevi. A silent mutation/polymorphism in KIT exon 13 was found in one PAM.

Conclusion

Despite the high level of KIT immunostains in conjunctival PAM and melanoma, this parameter seems not to be a good predictor for the presence of molecular mutations. KIT-activating mutations should be considered an uncommon event in these tumors.

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