Salivary Gland Mucinous Adenocarcinoma With Minor (Mammary Analogue) Secretory and Low-Grade In Situ Carcinoma Components Sharing the Same ETV6-RET Translocation and With No Other Molecular Genetic Aberrations Detected on NGS Analysis
Abstract
In 2016, we published in this journal a hitherto undescribed composite salivary gland carcinoma arising in the left parotid gland in a 54-year-old woman. The tumor had a minor mammary analogue secretory carcinoma component (MASC), with a morphologically entirely different mucinous adenocarcinomatous component and a focal, morphologically nondescript, low-grade intraductal (in situ) component.
On fluorescence in situ hybridization (FISH), w detected breaks in the ETV6 gene in all the 3 different components. However, RT-PCR failed to reveal an ETV6-NTRK3 fusion.
On immunohistochemistry, the entire conventional MASC and patchy mucinous adenocarcinoma tumor cells expressed mammaglobin, while the in situ component was negative. S-100 protein was only expressed by the MASC component.
Using the TruSight tumor 170 assay (Illumina, San Diego, CA) on the NextSEq. 500 sequencer (Illumina) following the usual manufacturer's protocols, we have subsequently further analyzed the in situ and invasive component (MASC mixed with mucinous adenocarcinoma components) separately. This molecular genetic study revealed the same ETV6-RET fusion (exon joining 6 to 12) in both samples.
No other molecular genetic aberrations were identified in the applied panel, which consists of 170 genes. The complete list of genes and mutations covered by this assay is shown in Supplemental Table 1.