ASCO 2017: Incidence of intrathoracic metastases detected by 68Ga-PSMA-11 PET in early stage prostate cancer

Chicago, IL ( Standard imaging in early stage prostate cancer (PC) has focused on detecting metastases within the abdomen and pelvis. The incidence of intrathoracic (IT) metastasis (lung, mediastinal, or supraclavicular) is unknown, but presumed to be negligible. Whole body 68Ga-PSMA PET has greater sensitivity compared to conventional imaging, enabling a more accurate estimation of IT metastasis.  

Dr. Rahul Aggarwal presented a study where newly diagnosed or biochemically recurrent (BCR) PC patients with apparent localized disease on standard imaging, were enrolled. This was a prospective study where all patients underwent 68Ga-PSMA PET imaging between June 2015 and January 2017 and were analyzed for incidence of IT metastasis (Clinical trial information: NCT02918357). Positive lesions were defined as uptake higher than blood pool. When appropriate, patients underwent confirmatory biopsy of the PSMA-avid IT lesions. This study’s objectives were to estimate the incidence of IT metastasis in the setting of newly diagnosed and BCR state; and to ascertain the long term clinical outcomes of patients with IT metastasis versus those without. 

Overall, 364 patients underwent 68Ga-PSMA PET imaging, including 121 (33%) patients with newly diagnosed PC and 243 (67%) patients with BCR. Median age was 70 (45-88). 145 patients (40%) had at least 1 PSMA-avid metastasis. PSMA-avid IT metastasis were detected in 20 patients (5.5% of overall cohort; 13.8% of those with ≥ 1 PET-positive metastasis), including 3 newly diagnosed (2.5%) patients and 17 (7.0%) patients with BCR. 9/20 patients (45%) had IT metastasis as the only detectable site of metastasis on PET. Biopsy of the PSMA-avid IT lesion was found to harbor PC in 5/6 patients (83%). Sites of detection included: supraclavicular node, n = 9 (2.5%); mediastinal node(s), n = 10 (3.6%), and visceral lung, n = 4 (1.0%). In the entire study cohort of 364 patients, 43% had a Gleason Score ≥ 8 at diagnosis, median PSA was 4.87 ng/mL (range: 0.04 – 83.7), and the median PSA doubling time was 6.2 months (range: 0.4 – 78.3) in patients with BCR. There were no significant differences in PSA, PSA doubling time, Gleason grade, or stage between patients harboring IT metastases versus those who did not. 

In summary, IT metastasis was found in 5.5% of patients. Higher serum PSA at time of imaging was associated with detection of IT metastasis. Further studies are warranted to validate these findings and determine the optimal strategy for the detection and treatment of IT metastases in newly diagnosed and biochemically recurrent PC. 

Presented By: Rahul Raj Aggarwal, MD, University of California San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, CA

Written By: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Toronto, Ontario, Canada
Twitter: @GoldbergHanan

at the 2017 ASCO Annual Meeting - June 2 - 6, 2017 - Chicago, Illinois, USA


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