Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2023

Evaluating the utility of 2-Deoxy-2-[F-18]fluoro-D-glucose Positron Emission Tomography/Computer Tomography in Cancer of Unknown Primary. (#236)

Tharani Sivakumaran 1 2 , Anthony Cardin 1 3 , Jason Callahan 4 , Hui Li Wong 1 2 , Richard Tothill 1 5 6 , Rod Hicks 4 7 , Linda Mileshkin 1 2
  1. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia
  2. Medical Oncology, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  3. Cancer Imaging , Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  4. Melbourne Theranostic Innovation Centre, Melbourne, VIC, Australia
  5. Department of Clinical Pathology, University of Melbourne, Melbourne, VIC, Australia
  6. University of Melbourne Centre for Cancer Research, University of Melbourne, Melbourne, VIC, Australia
  7. The University of Melbourne Department of Medicine, St Vincent’s Hospital, , Melbourne, VIC, Australia

Aims: We aimed to describe the Peter MacCallum Cancer Centre experience with 18F-FDG PET/CT in cancer of unknown primary (CUP) with respect to detection of a primary site and its impact on management. Secondary aim was to compare overall survival (OS) in patients with and without a detected primary site.

Methods: Retrospective analysis of CUP patients identified from medical oncology clinics and PET/CT records between 2014-2020. Clinicopathologic, treatment details and genomic analysis were used to determine the clinically suspected primary site and compared against two independent blinded nuclear medicine specialist 18F-FDG-PET/CT reads to determine sensitivity, specificity, accuracy and detection rate of primary site.

Results: 147 patients were identified of whom 65% underwent molecular profiling. Median age at diagnosis was 61 years (range 20-84) with 93% being ECOG 0-1 and 82% classified as unfavourable CUP subtype as per ESMO guidelines. 18F-FDG-PET/CT detected a primary site in 41%, changed management in 22% and identified previously occult disease sites in 37% of patients. The sensitivity, specificity and accuracy were 61%, 34% and 52%, respectively. Median OS for all patients was 17.4 months. Median OS in patients with a detected primary site on 18F-FDG-PET/CT scan concordant with clinicopathological and genomic information was 19.8 months compared with 8.5 months in patients without a detected primary site (p = 0.008). Multivariable analysis of survival adjusted for age and sex remained significant for identification of potential primary site (p=0.007), favourable CUP (p<0.001) and ECOG ≤ 1 (p<0.001).

Conclusions: 18F-FDG-PET/CT plays a complementary role in CUP diagnostic work-up and in 41% of cases a potential primary site was identified. OS is improved with primary site identification, demonstrating the value of access to a diagnostic 18F-FDG-PET/CT scan for CUP patients.