Model unable to identify focal therapy candidates

Boston-The development of a model for identifying prostate cancer patients who may be appropriate candidates for hemi-ablative focal therapy remains a work in progress for researchers at Memorial Sloan Kettering Cancer Center (MSKCC).

In a poster presented at the AUA annual meeting in Boston, they reported that the Kattan nomogram score and a magnetic resonance imaging extraprostatic extension (MRI EPE) score ≥3 were independent predictors of extensive disease. A multivariable model incorporating those variables, however, did not place patients into a low enough risk group where hemi-ablative therapy would be indicated.

“There is increasing interest in focal therapy for prostate cancer, but it remains difficult to appropriately select men who should be eligible for this procedure,” said Toshikazu Takeda, MD, urologic oncology fellow, MSKCC, New York, and instructor of urology, Keio University School of Medicine, Tokyo.

“Our aim is to analyze data from men who have undergone radical prostatectomy in order to identify preoperative factors that are predictive of extensive disease,” added Dr. Takeda, who worked on the study with Karim A. Touijer, MD, MPH, and colleagues.

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The initial analyses included data from 98 men who were diagnosed with unilateral prostate cancer by minimum 10-core biopsy, met the focal therapy consensus meeting inclusion criteria (PSA <15 ng/mL, clinical stage T1c-T2a, Gleason score 3+3 or 3+4), underwent radical prostatectomy at MSKCC between 2000 and 2014, had tumor maps from whole-mount slides, and underwent preoperative 3T multiparametric MRI. PI-RADs version 2 was used to generate an MRI tumor score, and both EPE and seminal vesicle involvement (SVI) were scored on a scale of 1 to 5 based on the MRI.

Thirty-nine of the men (40%) were determined to have extensive disease defined by having at least one of the following findings on the tumor map and radical prostatectomy pathology: Gleason pattern 4 or 5 in both lobes, EPE, SVI, or lymph node involvement. Of the 39 men, 32 had Gleason pattern 4 or 5 bilaterally, 16 had pathologic stage ≥T3a disease, and one had lymph node involvement.

Preoperative characteristics evaluated for their association with extensive disease included age, % positive cores, prostate volume, bilateral MRI tumor score ≥3, MRI EPE score ≥3, SVI score ≥3, and Kattan nomogram risk of recurrence after RP.

Next: Model adds no value

Model adds no value

A decision curve analysis was conducted to assess the clinical utility of a predictive model. Specifically, it examined whether the model provided a net benefit compared with a treat-all strategy when setting the threshold probability of having extensive disease at <20%. The analysis showed the model added no value.

Dr. Takeda suggested that the study was limited by small sample size.

“We identified 770 patients who were diagnosed with unilateral prostate cancer, met the criteria for focal therapy, and underwent radical prostatectomy, but only 98 of them had mpMRI data and tumor maps,” he said.

In addition, Dr. Takeda noted that in the years covered by the study period, biopsy was performed prior to MRI. That sequence can result in artifacts in the MRI.

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“Approximately 40% of our patients with an MRI tumor score of 4 or 5 had a biopsy negative lobe. To avoid a confounding effect from biopsy, the MRI should be done first,” he said, adding that a future study may include a more contemporary group of patients from MSKCC who have undergone targeted biopsy after MRI.

Dr. Takeda also believes that a future study designed to identify variables for selecting appropriate candidates for hemi-ablative focal therapy might use less stringent criteria for defining extensive disease.

“The definition used in the present study included all Gleason pattern 4 or 5 in bilateral lobes. However, it may be appropriate to treat some men who have a very small volume of Gleason 4 disease with hemi-ablation followed by active surveillance,” Dr. Takeda told Urology Times.

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