Abstract 3397: Post-mortem examination of an aggressive case of medullary thyroid cancer characterised by catastrophic genomic abnormalities

Catastrophic genomic alterations may drive aggressive cancer phenotypes. We describe a diagnostically challenging and rapidly fatal case of medullary thyroid carcinoma (MTC) occurring in a young, morbidly obese man presenting with diffuse bone marrow involvement and disseminated intravascular coagulation. Whole-exome (WES) and shallow whole-genome sequencing (sWGS) were carried out for the primary tumour, adjacent normal, bone marrow tissues, multiple metastases and blood samples derived from the patient. We identified three germline single nucleotide polymorphisms (SNPs) within the RET proto-oncogene that remained undetected using routine hospital genetic testing procedures. One variant (L769L) has been previously reported to be associated with aggressive MTC presentation yet remains untested for in the routine diagnosis of MTC. Supported by findings from both WES and sWGS, we report for the first time in thyroid cancer on the occurrence of a “chromothripsis-like pattern”, which involved shattering of chromosome 4 leading to complete abrogation of normal chromosomal function, along with dramatic widespread copy number aberrations across both primary tumour and bone marrow samples. Based on the somatic variants identified, we describe the evolutionary pathway of the case, showing that bone marrow metastasis occurred separately to other metastatic sites. The presence of disease-associated SNPs within the RET proto-oncogene supports their inclusion as part of routine genetic testing for MTC cases. The copy number aberrations and chromothripsis-like pattern affected a much broader range of genes than single mutations and may have led to the widespread chromosomal instability evident, possibly contributing to the rapid fatal course of the case. These results provide a rationale for the application of comprehensive genomic analysis of cancers presenting with unusual and aggressive phenotypes to facilitate more appropriate therapeutic options and diagnoses. Citation Format: Darran P. O'Connor, Sudipto Das, Deirdre Kelly, Bruce Moran, Kathleen Han, Niall Mulligan, Ciara Barrett, Patrick Buckley, Peter McMahon, J McCaffrey, Henrik van Essen, Kate Connor, Bauke Ylstra, Diether Lambrechts, William M. Gallagher, Catherine M. Kelly. Post-mortem examination of an aggressive case of medullary thyroid cancer characterised by catastrophic genomic abnormalities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3397. doi:10.1158/1538-7445.AM2017-3397