New Entry in 'Burgeoning Field' of Prostate Cancer Therapy

Gland Downsized From Walnut to Lentil

Nick Mulcahy

May 10, 2019

CHICAGO — The prostate is not large — about the size of a walnut, to use a common analogy.

A novel ablative technology for prostate cancer doesn't leave much of that behind after a typical 50-minute treatment, reducing prostate size by 90% (from 41 to 4 cubic centimeters), according to a new study here at the 2019 American Urological Association annual meeting.

Magnetic resonance-guided transurethral ultrasound ablation (TULSA; Profound Medical) is a relatively new entry into the "burgeoning field within localized prostate cancer trying to come up with newer, better ways of treating it," said lead author Scott Eggener, MD, urologist, University of Chicago, at an AUA press briefing.

The treatment is not yet available in the United States, but is used in some European centers. The company recently submitted its 501K application to the FDA for potential approval.

In the new phase 2 study at 13 institutions in five countries, nearly all of the 115 men (96%) met the primary endpoint of PSA reduction ≥75%. Eggener acknowledged that other technologies that fully ablate the prostate have yielded prostate-specific antigen (PSA) reductions "in this ballpark."

Pretreatment, 72 (63%) of 115 men had Grade Group 2 (GG2), also known as Gleason score 3+4 or higher.

The study group's posttreatment median PSA was 0.34 ng/mL, which is "really darn low, suggesting [TULSA] did a really good job of ablating prostate tissue," said Eggener.

Alan Priester, PhD, urology researcher, University of California, Los Angeles, called the new technology "very exciting" and the early results "quite promising."

However, the new study yielded a "worrying statistic," he said.

" Despite more than 90% of the gland being destroyed, 36% of men had evidence of cancer on follow-up," Priester told Medscape Medical News. On a more positive note, "much of this was clinically insignificant," he added.

This was a reference to the fact that 64% of the men were cancer-free at the mandatory 1-year biopsy, a secondary outcome.

However, for the subset of men at study entry with Gleason Grade (GG) 2, also known as Gleason score 3+4 or higher, the results were better: 79% were free of cancer a year later.

Priester said that a more judicious patient selection might help reduce recurrence (such as exclusion of patients with large calcifications or suspicion of extra capsular extension). 

TULSA is different from high intensity focal ultrasound (HIFU), employing a peripheral stream of ultrasound with a continuous sweeping rotation. HIFU's ultrasound comes through the rectum to the prostate; both technologies ablate a large portion of the prostate.

Eggener told reporters that the "holy grail" of organ-confined prostate cancer treatment is to destroy almost all of the tissue while limiting damage outside of the gland, to protect sexual and urinary function.

"As best we know, the way we get erections is through nerves that are on the outside of the prostate," Eggener noted.

Another primary aim is to spare the urethra, which goes through the center of the prostate, to avoid urinary symptoms.

Eggener's "utopian" vision for men, once they are done childbearing, is a magic bullet pill that they could take "to make the prostate go away" and thereby avoid infections, enlargement, and cancer.

Adverse Events and More Details

The TULSA procedure takes place in an MRI suite, under general anesthesia, with a team that includes a urologist and radiologist, said Eggener. The cancer and prostate are mapped via a transuretheral probe. The patient also has a subrapubic tube that goes through the abdomen into the bladder and stays in place for approximately 2 weeks after the treatment.

In the new study, median age was 65 years and PSA 6.3 (4.6 - 7.9) ng/mL. Median treatment delivery time was 51 minutes. That impressed Priester.

"Radical prostatectomy takes hours, as do many MR-guided interventions such as HIFU or laser ablation," he said.

The reported treatment time did not account for the time spent on patient prep and MR localization. Nonetheless, Priester said, "it is still an impressive reduction in procedure time, which could help lower procedure costs and improve safety."

Grade 3 adverse events occurred in 9 (8%) men, including infections (4%), urethral stricture (2%), urinary retention (2%), urethral calculus and pain (1%), and urinoma (1%), all resolved. There were no rectal injuries or grade 4 or higher events.

Of 112 men with 1-year continence data, 1% were incontinent (more than 1 pad/day), daily leakage increased 4%, and 8% wore a pad. Median International Prostate Symptom Score was unchanged at 1 year.

"Despite treating of the entire prostate gland, the investigators managed to preserve urinary continence and function in almost all patients," said Priester. "From a technological standpoint this is particularly impressive, considering that treatment was delivered transurethrally but [yet] they managed to spare the urethra from treatment."

At 1 year, 20% of patients had grade 2 erectile dysfunction, median change in International Index of Erectile Function (IIEF-5) was -3 (-13 to 0, n = 105), and 69 (75%) of 92 patients maintained erections sufficient for penetration (IIEF Q2 ≥ 2).

Priester commented that the reported impotence rates were below par. "While this is better than radical prostatectomy, it is worse than reported values for most focal treatments such as focal HIFU or hemi-gland cryoablation," he said.

Eggener is a consultant for Profound Medical, which sponsored the study. Priester is a consultant for Avenda Health.

2019 American Urological Association annual meeting: Abstract LBA26. Presented May 5, 2019.

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