The repertoire of genetic alterations in salivary duct carcinoma including a novel HNRNPH3-ALK rearrangement.

Salivary duct carcinoma (SDC) is a rare, aggressive malignancy with limited treatment options and poor outcome. Twenty-nine primary resected SDC, including 15 SDC de novo (SDCDN), and 14 SDC ex pleomorphic adenoma (SDCXPA) were subjected to the massive parallel sequencing assay (MSK-IMPACT) targeting 287 to 468 cancer-related genes. TP53 was the most frequently altered gene (69%). TP53 mutations and ERBB2 amplification were more frequent in SDCXPA than in SDCDN (P = .0007 and P = .01, respectively). Potentially targetable mutations were detected in 79% (23/29) of SDC involving ERBB2 (31%), PIK3CA (28%), HRAS (21%), ALK (7%) and BRAF (3%), and 22% (5/23) of those cases harbored possible primary resistance mutations involving CCNE1, NF1 and PTEN. A novel HNRNPH3-ALK rearrangement was found in one SDCDN. In another case, EML4-ALK fusion detected in the primary tumor was associated with ALK G1202R secondary resistance mutation in the post-treatment metastasis. A germline analysis of the DNA repair genes revealed a case with a pathogenic BRCA1 E23fs germline variant. SDCDN and SDCXPA are genetically distinct. Although the majority of SDC may be amenable to molecular targeted therapy, concurrent possible resistance mutations may be found in a significant minority of cases. A broad genomic profiling is necessary to ensure detection of rare but clinically actionable somatic alterations in SDC.