2018 Congress of the Mexican Association of Oncological Urology

Is There a Role for PET/CT Imaging in Decision Making for Localized Prostate Cancer Treatment?

Acapulco, GRO, Mexico (UroToday.com) Arturo Delgado Herrera, MD, first reviewed conventional imaging techniques used for staging in localized prostate cancer and the indications of these studies based on a risk stratification model. He recognized the caveats of conventional imaging techniques such as; the limited sensitivity and specificity for the detection of bone metastasis and positive lymph nodes and how positive findings are associated with PSA level, initial Gleason score, and clinical T stage. The only current indication in the 2018 NCCN guidelines for preoperative PET/CT is to evaluate equivocal lesions in a conventional bone scan with F-18 NaF. 

The role of PET/CT imaging prior to definitive treatment is still unclear and he outlines uses of the current radiotracers available:

  • C-11 Choline, FDA cleared, may be used for detection of biochemically recurrent small-volume disease. 
  • F-18 Fluciclovine, FDA cleared, a synthetic amino acid may also be used for detection of biochemically recurrent small volume disease in soft tissues. 
  • Ga-68 PSMA, an increasingly popular tracer used worldwide that provides better detection of recurrences at lower PSA levels with better sensitivity (76-86%) and specificity (86-100%) than other FDA approved agents.
  • F-18 NaF has a better sensitivity (87-100%) and specificity (62-89%) for the detection of bone lesions when compared with conventional bone scans. 
He then recognized the importance of the “Will Rogers Phenomenon” stating that PET/CT use may increase the detection of cancer metastasis before these lesions become clinically evident and this bias may be falsely interpreted as a treatment effect.

A compelling argument was made for the use of PET/CT with Ga-PSMA for primary lymph node staging in high-risk prostate cancer. He cited a retrospective multicenter study of 51 patients where there was considerable upstaging from the clinical to the pathological stage and the value in predicting occurrence of lymph node (LN) metastasis in patients with ≥ 15 node harvest was significant, with a sensitivity of 66.6%, specificity of 88%, accuracy of 81%, positive predictive value of 72.7% and negative predictive value of 84.6%. These results are comparable with other published data and this suggests that PET/CT with PSMA may be superior to conventional studies for the detection of LN metastasis in the initial staging of patients with high risk localized prostate cancer. 

The RADAR III guidelines recommend the use of new diagnostic studies when findings are equivocal or undetermined in conventional studies and they recommend that these studies should be considered for the initial staging of patients with high-risk disease or suspected locally advanced disease. 

PET/CT with PSMA is not yet approved by FDA in the United States but its use has been increasing in many hospitals throughout the country. (see Figure 1)

Figure 1: 
To conclude, he stated that conventional bone scan and abdominal-pelvic CT scan are standard of care for the initial staging in patients with intermediate or high-risk disease but have intrinsic limitations, primarily a limited sensibility and specificity for the detection of positive lesions. PET/CT with F-18 NaF should be used to evaluate equivocal lesions in bone scans and the use of other tracers for primary staging are unclear at the moment, however, PSMA is showing promising results in selected individuals. 

Presented by: Arturo Delgado Herrera, MD, Associate Professor of Genitourinary Oncology and Oncological Sciences from the UMAE Hospital de Oncología Centro Médico Nacional Siglo XXI

Written by: Adrián M. Garza-Gangemi, MD, Resident of Urology, Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, Mexico @aggangemi & Dr Ashish M. Kamat, Professor of Urologic Oncology, MD Anderson Cancer Center, Houston, TX at the 2018 Congreso de la Asociación Mexicana de Urología Oncológica – July 25-28, 2018, Acapulco, GRO México
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