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.