Poster Presentation ESA-SRB-APEG-NZSE 2022

The Clinical Utility of PET scanning in Medullary Thyroid Cancer (#286)

Matti L Gild 1 2 , Shejil Kumar 1 , Talia Fuchs 3 , Anthony Glover 2 4 , Venessa HM Tsang 1 2 , Geoff Schembri 5 , Anthony J Gill 2 3 , Roderick J Clifton-Bligh 1 2 6 , Jeremy Hoang 5
  1. Endocrinology Department, Royal North Shore Hospital, St Leonards, NSW, Australia
  2. Sydney Medical School, University of Sydney, Sydney
  3. Department of Anatomical Pathology, Royal North Shore Hospital, Sydney, NSW
  4. Endocrine Surgery, Royal North Shore Hospital, Sydney, NSW, Australia
  5. Nuclear Medicine, Royal North Shore Hospital, St Leonards, NSW, Australia
  6. Kolling Institute of Medical Research, St Leonards, NSW, Australia

 

Background:  Somatostatin receptor (SSTR) functional imaging with PET-CT has broadened the diagnostic and staging capabilities for medullary thyroid cancer (MTC). 68Ga-DOTATATE is a radiotracer with a high affinity for type 2 somatostatin receptors (SSTR2) expressed in many but not all MTCs.   Correlation between 68Ga-DOTATATE-PET/CT avidity and in-vitro SSTR2 immunohistochemistry has been established in some neuroendocrine tumours (NETs) but not MTC.  The utility of 68Ga-DOTATATE-PET/CT and 18F-FDG-PET/CT imaging in predicting MTC prognosis is also unknown. 

 

Methods: In this single centre retrospective study, 37/99 (37%) of MTC patients underwent 68Ga-DOTATATE-PET/CT imaging; of these, 13 (35%) had contemporaneous 18FDG-PET/CT. 68Ga-DOTATATE-PET/CT and 18FDG-PET/CT scans were assessed by two experienced nuclear medicine physicians.  SUVmax, SUVmean, metabolic tumour volume (MTV) and total lesion activity (TLA) were assessed for both PET radiotracers. Tumours archived in formalin-fixed paraffin-embedded blocks were constructed into tumour microarrays and immunohistochemistry (IHC) for SSTR2A and Ki67 were scored.  

 

Results: SSTR2A expression was measured by IHC in the primary tumour; 37/99 (37%) had at least some and 62/99 (63%) had no detectable SSTR2A expression.  There was no difference in overall survival, calcitonin doubling time or age between SSTR2A +/- tumours.  Of the 37 patients with 68Ga-DOTATATE-PET/CT, 32/37 (86%) had avid disease, most commonly in nodal metastases. Ki67 in the primary tumour significantly correlated with 68Ga-DOTATATE MTV (p=0.004) and TLA (p=0.007).  SSTR2A IHC did not correlate with 68Ga-DOTATATE avidity. Comparison with 18FDG-PET showed 6/13 patients had 18FDG>68Ga-DOTATATE avidity, 3/13 concordant and 4/13 68Ga-DOTATATE>18FDG avidity. Disease-specific deaths were only seen in the 18FDG >68Ga-DOTATATE avid cohort. Shorter survival was associated with TLA>20 (p=0.04) but not with RET alteration status, calcitonin, or 68Ga-DOTATATE SUVmax or mean.  

 

Conclusion: Assessment of TLA from 68Ga-DOTATATE PET/CT may predict survival. SSTR2A IHC did not correlate with 68Ga-DOTATATE avidity. Metastatic disease may be optimally assessed by concurrent 18FDG and 68Ga-DOTATATE imaging.