Abstract 4844: High throughput detection of PRKD1 mutations in salivary gland tumors usingin situmutation detection in tissue microarrays

Recently, unique activating mutations in PRKD1 were observed in salivary gland polymorphous low-grade adenocarcinoma (PLGA). PRKD1 is a serine-threonine kinase that participates in important cell functions such as survival, adhesion, and migration. PLGA is a salivary gland tumor that usually shows indolent clinical presentation. Due to morphological similarities within different subtypes of salivary gland neoplasms, differential diagnosis may be puzzling. Although salivary gland cancer is a rare disease (around 3,000 new cases per year in the USA), the gravity of the disease should not be undermined. Currently, the salivary gland cancer biology is poorly understood. Comprehending the molecular biology of this cancer is instrumental in improving the diagnosis and prognostic prediction of this disease. Our goal is to assess the incidence of c.2130A>T and c.2130A>C PRKD1 mutations in different salivary gland tumors by a high throughput mutation detection technique. We first assessed the c.2130 PRKD1 point mutations in 8 PLGA cases using conventional Sanger sequencing. Hotspot mutations were present in 75% (6/8) of the samples. Subsequently, we built tissue microarrays slides that included the following: 5 PLGA, 54 adenoid cystic carcinomas, 30 mucoepidermoid carcinomas, 14 acinic cell carcinomas, 6 adenocarcinomas not otherwise specified, 34 pleomorphic adenocarcinomas, 3 mammary analogue secretory carcinomas, and 1 salivary duct carcinoma. Additional sample collection is ongoing. We optimized a recently described in situ mutation detection to directly visualize single mutations with microscopy in fixed cells and tissue sections. The technique is based on in situ proximity ligation assays that utilize sequence specific probes. Ligation of the padlock probe will only occur if there is a perfect match between the probe and the target. The probes are labeled with fluorophores that allow generated signals to be visualized as bright spots with a fluorescence microscope. This technique allows exact quantification of the detected target molecules while identifying each individual signal (mutant or wild type) within the tissue sections. Once the methodology is validated to detect these mutations, it will allow us to quickly analyze a cohort of salivary gland neoplasms which have been already prepared as tumor microarrays. Additionally, this technique will open new avenues to analyze other mutations in different tumor cohorts already prepared as tumor microarray slides. In the context of salivary gland tumors, differentiating distinct primary tumors subtypes and/ or metastasis from primary tumors with other sites of origin would be invaluable for clinical decisions. Citation Format: Piotr T. Wysocki, William H. Westra, Shahnaz Begum, David Sidransky, Mariana Brait. High throughput detection of PRKD1 mutations in salivary gland tumors using in situ mutation detection in tissue microarrays. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4844. doi:10.1158/1538-7445.AM2015-4844