Multiparametric MR imaging before a transrectal ultrasound (US)-guided targeted biopsy (TB) improves detection of prostate cancer over the standard extended systematic biopsy (SB), according to a study published in the August issue of Radiology.

TB detected 15 percent more clinically significant cancers than SB, with those cancers going undetected had the patient not undergone prebiopsy MR imaging and TB, explained Philippe Puech, MD, PhD, of the University of Lille in France, and colleagues.

“These ‘missed’ cancers were mainly located in the anterior regions of the gland: Of the 18 clinically significant [prostate cancer] lesions diagnosed with TB and not with SB, only four were located in the posterior part of the gland,” wrote the authors.

Standard SB only takes samples of the posterior part of the prostate, which risks underdiagnosis of anterior lesions. About 18 percent of cancers in unselected patients suspected of prostate cancer are anterior lesions, according to Puech and colleagues.

To compare performance of MR-TB with SB, the researchers conducted a multicenter prospective study of 95 patients suspected of prostate cancer from May 2009 to January 2011. All patients had a suspicious abnormality at prebiopsy MR.

Study participants underwent a 12-core SB and a four-core TB with transrectal US guidance. The four-core TB was split between two methods. Two cores were targeted by a physician who reviewed the MR imaging results before the procedure and used this knowledge to select the area for TB. This method is called cognitive targeting (TB-COG). The other two cores of the TB were aimed using US-MR fusion software (TB-FUS).

Results showed the positivity rate for prostate cancer was 59 percent for SB and 69 percent for TB. For clinically significant cancers—defined as any 3 mm or greater core cancer length or any cancer greater than Gleason score 3—the positivity rates for SB and TB were 52 percent and 67 percent, respectively.

TB was able to diagnose cancer in 16 patients with negative SB results, and of the 51 patients with both positive SB and TB results, 24 percent had their Gleason score upgraded on the basis of TB.

Positivity for cancer varied between TB methods, with TB-COG detecting 37 cancers and TB-FUS detecting 42. However, neither method was superior for Gleason score assessment, noted Puech and colleagues.

“[O]ur data in this prospective multicenter study indicate that prebiopsy MR imaging combined with transrectal US–guided TBs increase the performance of biopsies conducted without knowledge of imaging results in diagnosing clinically significant and anterior [prostate cancer] lesions.”