18Fluorocholine-PET/CT demonstrates better clinical utility than conventional prostate imaging

SAN FRANCISCO — First-line imaging with ¹⁸fluorocholine-PET/CT demonstrated more clinical utility than conventional imaging for identifying prostate lesions with a high impact on patient management, according to results of a randomized trial presented at Genitourinary Cancers Symposium.

However, researchers did not observe an increase in prognostic performance with the different imaging modality, and both approaches appeared to have a poor negative predictive value.

“The evidence base for managing prostate cancer is based on ‘conventional’ imaging with CT abdomen/pelvis and ^99mTc-Whole Body Bone Scan,” Scott Williams, BSc, MBBS, MD, FRANZCR, radiation oncologist in the uro-oncology service at Peter MacCallum Cancer Centre in Victoria, Australia, said during his presentation. “However, we know that men with high-risk disease who are clear on conventional imaging still suffer a very high proportion of progression. “Also, prostate cancer has largely missed out on the fervor around [fluorodeoxyglucose]-PET, which has been really transformative in most other areas of oncology,” he added.

Choline metabolism had become a pathway of interest in prostate cancer, Williams added.

“Choline is a precursor of phosphatidylcholine, a component of cell membranes, and prostate [magnetic resonance] spectroscopy is known to show choline accumulation,” he said. “The rationale for this study was based on the allure of increased sensitivity.”

Researchers compared ¹⁸Fluorocholine-PET/CT, or FCH-PET/CT, with conventional imaging to determine whether it could capture more staging information, whether increased sensitivity might translate into changes in management, and whether this method of imaging could be a first-line “one-stop shop.”

The analysis included 108 men with newly diagnosed prostate cancer (44%) or a suspected prostate cancer recurrence. Researchers randomly assigned men to conventional imaging or FCH-PET/CT. Men without metastases detected with their assigned imaging modality would go on to receive the other type of imaging as second-line imaging, and both types of imaging at a 6-month follow-up.

Overall, 43 men (median age, 67.5 years) underwent conventional imaging only, 44 (median age, 71 years) underwent FCH-PET/CT only and 44 (median age, 70 years) underwent both.

High management impact — defined as a change from radical to palliative intent (or the reverse) or a change in primary treatment modality — served as the study’s primary endpoint. Secondary endpoints included any management impact, incremental value, equivocal scan rates and negative predictive value.

Median follow-up was 43 months.

Imaging impacted clinical management in 32.4% (95% CI, 23.7-42.1) of men, primarily after first-line imaging (n = 30).

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High-impact changes occurred for a greater proportion of men assigned FCH-PET/CT than conventional imaging (27.8%; 95% CI, 16.5-41.6 vs. 11.1%; 95% CI, 4.2-22.6; P = .032).

All management changes also were more frequent in the FCH group (35.2%; 95% CI, 22.7-49.4 vs. 20.4%; 95% CI, 10.6-33.5), but this difference did not reach statistical significance.

Four men — all of whom were in the conventional imaging group — had metastases detected and did not go on to second-line imaging.

Four men originally randomly assigned to conventional imaging and one man assigned to FCH-PET/CT demonstrated an incremental high management impact by crossing over to second-line imaging with the other modality.

After both lines of imaging, the final management plan was dictated by the first-line imaging results in 98.1% (95% CI, 90.1-100) of FCH-PET/CT cases and 92.6% (95% CI, 82.1-97.9) of conventional imaging cases.

“It’s not that different, but that does imply that if you’re going to replace the combination of CT and bone scan with a single PET scan, you’re unlikely to lose much in the way of management information,” Williams said.

After follow-up imaging, researchers analyzed 172 matched patients of conventional and FCH-PET/CT imaging.

Researchers reported a 23.5% (95% CI, 15-34) equivocal imaging rate of conventional imaging as first-line imaging, which was significantly higher than the 4.6% (95% CI, 1.2-11.4) rate for FCH-PET/CT as first-line imaging (P = .0003).

After a median follow-up of 46.6 months, 82 men had undergone repeat imaging, 63 of whom had progressed clinically or radiologically.

A total of 26.3% (95% CI, 13.9-41.2) of men with initial N0M0 staging remained progression free at 7 years; this rate did not differ significantly between the random assignment groups.

Among those identified with N1M0 disease at first-line imaging, researchers reported significantly longer median PFS among those originally assigned to FCH (32 months; 95% CI, 2-68 vs. 3 months; 95% CI, 1-16; P = .05); however, overall failure rates appeared similar between the groups.

“However, ultimately, they all end up in the same place, and this is just a clear illustration of the lead-time bias or stage migration,” Williams said.

Researchers calculated a concordance index for TNM stage of 0.624 for conventional imaging and 0.635 for FCH-PET/CT staging, which indicated FCH did not significantly improve TNM staging.

“We thought we were really clever using management impact as a primary endpoint, but I would caution anyone in using it without clear demonstration of betterment of outcomes for patients,” Williams said. “Thirty percent of these men had a management change, but we can’t actually demonstrate any difference in outcome.” – by Alexandra Todak

Reference:

Williams S, et al. Abstract 2. Presented at: Genitourinary Cancers Symposium; Feb. 14-16, 2019; San Francisco.

Disclosures: Williams reports travel accommodations or expenses from Astellas Pharma. Please see the abstract for all other authors’ relevant financial disclosures.