Clinically significant prostate cancer is found in a “non-negligible” number of men who have screening PSA levels of 1.8 or higher but less than 3.0 ng/mL, according to recent study findings. It remains unclear, however, if a delay in the diagnosis of these cancers until PSA levels rise to 3.0 ng/mL would lower the likelihood of cure.
The findings are from the population-based Göteborg-2 screening study. Among 17,974 participants, 6006 men with a median age of 55.9 years were included in the current analysis. Of these, 82% had a PSA level less than 1.8 ng/mL, 11% had a PSA level of 1.8 or higher but less than 3 ng/mL (low-PSA group; median PSA 2.1 ng/mL), and 6.3% had a PSA level of 3 or higher but less than 10 ng/mL (high-PSA group; median PSA 3.9 ng/mL). Another 0.5% had a PSA level of 10 ng/mL or higher. Patients in the low-PSA group were recommended to undergo magnetic resonance imaging (MRI). Men with positive MRI findings had 4 targeted biopsies from each MRI-visible lesion.
Prostate cancer was found in 64 patients (41%) with positive MRI findings in the low-PSA group, the investigators reported in European Urology. Of these, 33 (21%) had Gleason 6 tumors (insignificant cancer) and 31 (20%) had Gleason 7 or higher tumors (significant cancer). In the high-PSA group, prostate cancer was detected in 61 patients (56%), including 26 (24%) with Gleason 6 tumors and 35 (32%) with Gleason 7 or higher tumors.
“These results are in-line with previous knowledge of prostate cancer incidence at low PSA levels” said study corresponding author Fredrik Möller, MD, of Skövde Hospital in Skövde, Sweden.
He added, “Our study indicates that MRI could be used as a selection tool to reduce prostate cancer overdiagnosis at lower PSA values, but would lead to a large increase in MRI [use]. We hope our future planned study comparing PSA cutoff of 3 ng/mL to a PSA cutoff of 1.8 ng/mL will show robust evidence regarding the benefits and harms of a lower PSA cutoff as an indication for MRI.”
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Due to the limited sensitivity and specificity of PSA screening, it has been proposed that MRI be part of first-line screening for prostate cancer. However, the high costs, limited availability, and large inter-reader variability are significant barriers.
The main strength of the current study is its large, population-based design with a relatively high participation rate. “The results should therefore be generalizable to a screening situation,” Dr Möller said. “The main limitations are the relatively young age group and results that are based on a single screening round and lack follow-up so far.”
Despite the strengths of the study, an important question remains as to whether the lead time in diagnosing these cancers (PSA 1.8 or higher versus PSA 3-10 ng/mL) has a major impact on outcomes, said Aly-Khan Lalani, MD, an assistant professor in the department of oncology at McMaster University in Hamilton, Ontario, Canada, who was not involved with the study.
“The larger point is that population-based screening, with rational guidance of when to leverage adjunctive tests and thereby risk stratify patients, will help ensure the most patients who warrant treatment are caught early,” Dr Lalani said. “By balancing this concept and also limiting overdiagnosis or excessive invasive testing, we can seek to provide survival benefits for our patients.”
Michael Whalen, MD, an associate professor of urology and chief of urologic oncology at George Washington University in Washington DC, noted that the number of positive MRI findings in the low-PSA group (25%) was surprisingly quite similar to the rate of positivity in the high PSA (3-10 ng/mL) group (31%). “However, significant cancer detection rates in the low-PSA group were about half of that in the high PSA group,” Dr Whalen said.
He pointed out that 37,887 men were invited to participate in the study, but only 17,806 opted to do so and 6006 were included in the current analysis. “Compared to other screening trials, this number is actually very low. The European Randomized Study of Screening for Prostate Cancer (ERSPC) trial included about 182,000 men, and the Prostate, Lung, Colorectal, and Ovarian (PLCO) trial in the United States included about 76,000 men. “Thus, the generalizability of the findings may be limited,” Dr Whalen said.
The study had a high biopsy compliance rate, so disease detection rates should be accurate, Dr Whalen said. Also, there was pathologic consensus from 3 different experienced uropathologists. “Although racial demographics were unpublished, it is likely predominately a Caucasian population,” he said. “How the lower PSA threshold of 1.8 ng/mL applies to a population with a higher proportion of African American men is unclear. Also, the influence of family history on acceptable PSA threshold was not explored.”
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