Malignant melanoma of the conjunctiva: a case report with examination of KIT and PDGFRA

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

PURPOSE

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

METHODS

Eighty-five conjunctival pigmented tumours [27 melanomas, 12 primary acquired melanosis (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 (tumour-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 nonlimbal tumour location and thickness of melanomas.

RESULTS

KIT stains were 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.

CONCLUSIONS

Despite the high level of KIT immunostains in PAMs and melanomas, this parameter seems not to be a good predictor of the presence of molecular mutations. KIT-activating mutations should be considered an uncommon event in this tumour.

Adenoid cystic carcinoma of the oral cavity: immunohistochemical study of four cases

Adenoid cystic carcinoma (ACC) in the oral cavity is rare, and no immunohistochemical studies of ACC in the oral cavity have been performed. This report describes the immunohistochemical study of four ACCs of the oral cavity. The male to female ratio was 1:3. The age was 43, 51, 59 and 64 years. The location was tongue (n=2), buccal mucosa (n=1), and gingiva (n=1). Histochemically, all ACCs were positive for neutral, carboxylated and sulfated mucins. Immunohistochemically, ACC was consistently positive for cytokeratin (CK) AE1/3, CK 34βE12, CK5/6, CK7, CK14, CK18, p63, CA19-9, c-KIT (CD117), PDGFRA, MUC1, and Ki-67 (labeling index: 5%, 15%, 20% and 40%). ACC was consistently negative for CK8, CK20, desmin, S100 protein, CD34, chromogranin, MUC2, MUC5AC and MUC6. Some ACCs were positive for CK CAM5.2 (3/4), CK19 (1/4), EMA (2/4), CEA (2/4), vimentin (3/4), α-smooth muscle actin (2/4), p53 (2/4), CD10 (2/4), and synaptophysin (1/4). These results may provide basic knowledge of ACC of the oral cavity.