According to Dr. Tunariu, imaging has an important role in all stages of prostate cancer, including treatment planning prior to radiotherapy or radical prostatectomy. In the space of local recurrence detection, she notes that mpMRI and PET-CT have similar performance and she often uses them in a complementary fashion. One of the most controversial spaces for prostate cancer imaging includes nodal staging and detection of lymph node metastasis. In her opinion, because of the low sensitivity, there is no indication for routine clinical use of either 11C-choline PET-CT or DW MRI for lymph node, in whom CT scan findings were normal. Additionally, 68Ga-PSMA-PET has been evaluated in nodal staging. In a study of 51 patients with high-risk disease, 68Ga-PSMA-PET demonstrated a sensitivity, specificity, accuracy, PPV and NPV for patients with ≥15 lymph nodes removed of 67%, 88%, 81%, 73%, and 85%, respectively . However, Dr. Tunario cautions that there are still limitations with lymph node staging with current imaging modalities. To illustrate her point, she presented a case of a patient with nodal recurrence after radical prostatectomy and salvage radiotherapy. On PSMA PET, this patient had 3 positive nodes, on ultra-small superparamagnetic particles of iron oxide (USPIO)-MRI 15 nodes were positive, however when the patient underwent extended salvage lymphadenectomy, 44 nodes were positive (with a post-operative PSA of 2.2 ng/mL). Several questions remain regarding the detection of nodal metastases according to Dr. Tunariu: (i) What is the gold standard? (ii) Do we need a biopsy of the M1 small nodes? Is it feasible to biopsy 2-8 mm lymph nodes? (iii) Does it impact PFS, MFS or OS if we treat all PET/MRI positive nodes?
Dr. Tunariu feels that imaging of bone metastases with whole-body MRI with DWI has the opportunity to improve lesion detection, with >90% sensitivity and specificity. In a recent systematic review and meta-analysis assessing the utility of using MRI for the detection of bone lesions, 10 studies assessed 1,031 patients reporting a pooled sensitivity of 0.96 (95%CI 0.87-0.99) and pooled specificity of 0.98 (95%CI 0.93-0.99) . Although these results are excellent and suggest MRI could replace bone scintigraphy for detecting bone metastasis, there was significant heterogeneity in the studies and as such the results should be interpreted with caution. According to Dr. Tunariu, whole body MRI with DWI may represent a “one stop imaging shop”, including an MRI of the pelvis for local recurrence and bone lesions, and MRI of the spine to detect soft tissue lesions (ie. liver, ureteric), fractures, and bone metastases response. Dr. Tunariu cautions that one weakness of MRI is detecting subcentimeter lung metastases.
Dr. Tunariu concluded her talk with several important points for stratifying patient tailored imaging, (i) local staging improves detection of local disease recurrence; (ii) there are still unanswered questions with regards to nodal staging and oligometastatic treatment; (iii) current strategies, specifically whole-body MRI, demonstrate good performance in detecting bone metastases; (iv) MRI offers improved detection of soft tissue lesions; (v) when assessing imaging and the clinical scenario, be aware of PSA and disease discordance.
Speaker: Nina Tunariu, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, United Kingdom
Written By: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, Twitter: @zklaassen_md at the EAU - Update on Prostate Cancer – September 15-16, 2017, Vienna, Austria
1. Obek C, Doganca T, Demirci E, et al. The accuracy of 68Ga-PSMA PET/CT in primary lymph node staging in high-risk prostate cancer. Eur J Nucl Med Mol Imaging 2017 Jun 18 [Epub ahead of print].
2. Woo S, Suh CH, Kim SY, et al. Diagnostic performance of magnetic resonance imaging for the detection of bone metastasis in prostate cancer: A systematic review and meta-analysis. Eur Urol 2017 [Epub ahead of print].