October 16, 2009 — Clinicians should consider magnetic resonance imaging (MRI) for men who have elevated prostate-specific antigen (PSA) levels or some other "worrisome" prostate cancer variable, but who also have repeated negative biopsies.
This advice comes from the authors of a small Canadian study of patients with anteriorly predominant prostate tumors, which was published online October 8 in the British Journal of Urology International.
"We are not advocating the use of MRI in all cases, because this would be costly and a waste of resources," write the authors, led by Nathan Lawrentschuk, MD, Urologic Oncology Fellow at Princess Margaret Hospital Cancer Program, University Health Network in Toronto, Ontario.
However, when repeated biopsy sampling in a worrisome patient does not reveal a tumor, MRI is appropriate because tumors located on the top of the prostate could evade traditional diagnostic procedures, including ultrasound-guided needle biopsy, the investigators say.
"These men benefit from MRI, which guides the biopsy procedure with a high degree of accuracy," said Dr. Lawrentschuk in a press statement, referring to men with anterior tumors.
"Looking back over my career, I can recollect many men with a high PSA and a small prostate volume and repeat negative biopsies. In retrospect, I can see these men had anterior prostate tumors," principal investigator and coauthor Neil Fleshner, MD told Medscape Oncology.
Dr. Fleshner is head of the Division of Urology at Princess Margaret Hospital and professor of surgery at the University of Toronto.
The investigators specified that MRI should be reserved for men who have had either repeated negative anterior and transition zone biopsies or who have low-volume prostate cancer accompanied by some worrisome feature.
"Thus, men with a PSA level of more than 10 ng/mL and a velocity of more than 2 ng/mL per year, as well as small-volume higher Gleason grade disease" are those requiring closer attention, the authors write.
Dr. Fleshner said that it was not known what percentage of men with these characteristics will have anterior prostate tumors. "That's the Holy Grail," he said. However, an estimated 30% to 40% of prostate cancers originate anteriorly, he added.
New Syndrome is Proposed: PEATS
The new study consisted of 31 patients with anteriorly predominant prostate tumors (tumors with >70% anterior to the urethra) on MRI. The group was culled from a larger prostate MRI database of 821 patients at the hospital.
MRI was usually undertaken because of the presenting PSA level or PSA velocity, the authors write.
More than half of the group (17/31) had a mean of 2 previous negative biopsies and a median PSA level of 12 ng/mL before undergoing the MRI. The rest of the group (14/31) was on active surveillance for low-volume prostate cancer and had a median PSA level of 10 ng/mL before undergoing MRI.
MRI had a positive predictive value for anterior tumors of 87% (27/31). This is 1 of 2 "major findings of the study," say the authors.
"MRI can help direct biopsies to the anterior prostate with a high degree of accuracy," they summarize.
The second major finding is that patients with anterior predominant prostate tumors "appear to have more aggressive tumors than expected."
After reviewing their 31 patients and the literature, the investigators proposed that a subset of patients with anterior prostate tumors fits the description of a syndrome, which they call "prostate evasive anterior tumor syndrome," or PEATS.
The hallmark of PEATS is that the tumors are not only evasive but aggressive.
"All clinicians have experienced the scenario of patients with multiple negative sets of biopsies and then seemingly high-volume, high-grade disease diagnosed at some point in the near future," the authors write.
"In addition, a subset of men on active surveillance can have fairly rapid progression despite seemingly low-risk features. We believe that a proportion of men in these clinical scenarios have PEATS," they continue.
Evidence of aggressive tumors was found among the 31 patients in the study, 13 of whom went on to have a radical prostatectomy and a very high rate of positive surgical margins (54%), note the authors. Positive surgical margins are an indicator of aggressive biology, and the institutional rate at Prince Margaret Hospital is only 26%.
Not all anterior tumors are aggressive, and therefore not all qualify as PEATS, the author concede.
However, clinicians are advised to suspect PEATS when a patient has some worrisome prostate cancer variables, such as escalating PSA and a negative biopsy. PEATS might also be present in men with low-volume disease on active surveillance, they said.
"Knowing about PEATS may also be important for men already on active surveillance — patients with slow-growing prostate cancer who are being regularly monitored through PSA testing and biopsy. Every man does not need an MRI, but knowing about PEATS will help us identify those who do," said Dr. Fleshner.
More study is needed to better delineate the prevalence of PEATS and to provide information on how to better detect it, the investigators conclude.
The researchers have disclosed no relevant financial relationships.
BJU Int. Published online October 8, 2009. Abstract
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