Case 2: Cancer predisposition with germline pathogenic variant in SDHC and co-existing GIST and paraganglioma.
A 17-year-old male with known germline pathogenic variant in SDHCand metastatic GIST with lesions in the liver, peritoneum, and lungs was being treated with the tyrosine kinase inhibitor regorafenib. Biochemical monitoring showed progressive elevation in chromogranin A over a 12-month period, from 46 ng/mL to 505 ng/dL.68Ga-DOTATATE PET revealed an intensely avid lesion in the porta hepatis (Fig. 2), histologically confirmed to represent paraganglioma. This DOTATATE-avid paraganglioma was also FDG avid, but there were multiple FDG-avid metastatic GIST lesions remarkably negative by 68Ga-DOTATATE PET, indicating two functionally distinct tumor types co-existing in the same patient. The co-existence of two tumor types in the same patient would be unusual in most circumstances, but not in patients with underlying CPS. Complicating the discovery of a new paraganglioma was the heterogeneous pattern of18F-FDG uptake in the GIST lesions, resulting both from prior RF ablations and ongoing treatment with tyrosine kinase inhibitors, which are known to alter the pattern of FDG-uptake in GIST lesions 14,15.