CTNNB1 mutations in basal cell adenoma of the salivary gland

Basal cell adenoma (BCA) and basal cell adenocarcinoma (BCAC) are uncommon salivary gland tumors comprising proliferation of basaloid cells. Nuclear β-catenin expression and mutations in its encoding gene (CTNNB1) are reported to be specific to BCA. PIK3CA mutations are only found in BCAC not in BCA. However, in previous studies the number of cases was relatively small. The present study analyzed 44 cases of basal cell neoplasms to identify the CTNNB1 and PIK3CA mutation profiles in this rare salivary gland tumor.

The basic clinical features and detailed histological patterns of 41 BCA and three BCAC cases were analyzed. All basal cell neoplasms and a tissue microarray of adenoid cystic carcinoma (AdCC) were tested for β-catenin immunohistochemistry. CTNNB1, PIK3CA, and CYLD mutations were detected by PCR and Sanger sequencing in each case.

Nuclear β-catenin expression was present in 97.6% of BCA and 66.7% of BCAC cases but not in AdCC cases. CTNNB1 mutations were found in 60% of BCA but not in BCAC. None of the tested cases had PIK3CA mutations. CTNNB1 mutation trended to be more common in those cases having a predominant tubular or tubulotrabecular patterns (p = 0.059).

β-catenin immunohistochemistry is very useful for the differential diagnosis between BCA/BCAC and AdCC. CTNNB1 mutations are common in BCA, especially those with tubular or tubulotrabecular patterns.