This is a non-coverage policy for the 4Kscore assay (developed by OPKO;
marketed by BioReference Laboratory, NJ). This test is a laboratory developed
test (LDT) and has not undergone Food and Drug Administration (FDA) review or
scrutiny. Review of the available evidence is summarized below.  
  
The 4Kscore test consists of a panel of 4 kallikreins in blood that is
supposed to reduce unnecessary biopsy in men being considered for biopsy of
the prostate for potential cancer. The clinical features of this group are
poorly defined. The kallikreins consist of total prostate-specific antigen
(PSA), free PSA, intact PSA and kallikrein-related peptidase 2 (hK2). The
authors of the training and validation study1 claim that the panel of
kallikrein markers can predict high grade prostate cancer on a prostate biopsy
in previously unscreened men with elevated PSA. They also claim to have
replicated their previous findings where they claim that application of a
statistical model incorporating all 4 kallikreins leads to superior clinical
results compared with the current strategy of biopsying all men with elevated
PSA. These data suggest that the number of men undergoing biopsy could be
reduced to half using 20% or greater risk of any cancer as a tentative
threshold for biopsy, with approximately 20% of cancers remaining undetected
among previously unscreened men. However, most of these cancers would be low-
grade and low-stage cancers typically associated with over diagnosis, while
few high-grade cancers would be missed. They claim "a large number of
unnecessary biopsies can be avoided at the expense of only a small number of
men with advanced cancer being advised against biopsy, few of whom would have
high-stage or high-grade disease. Accordingly, application of our model as
part of PSA screening would reduce the harms associated with unnecessary
biopsy".  
  
Despite the claims offered by these authors, their study is significantly
flawed. Their model includes patients outside of the intended use population
(PSA > 10 ng/mL) and patients who previously were biopsied with no cancer
discovered. Furthermore, in their iteration of the formula it is unclear how
much hK2 contributes above using all the other components which are
commercially available. Total PSA contribution is very significant. The area
under the curve (AUC) of the full model is 0.821, and without the
incorporation of the hK2 the AUC is 0.806 with overlapping confidence
intervals. Throughout the studies there is 1) inconsistent use of PSA as a
threshold for biopsy; 2) significant changes to the methodology (use of
F(ab')2 fragments of the monoclonal capture antibodies); and 3) modification
of the algorithm. Furthermore, earlier data was generated on (usually) a 6
core sextant biopsy and likely does not reflect the tissue volume assessed in
American men.  
  
In a Swedish case-control study nested within a population-based cohort,2 the
4 kallikreins were combined into a statistical risk model based on the Vickers
validation that gives risk of any grade (or Gleason score=) cancer at prostate
biopsy. More than 12,500 men were followed for >15 years. PSA testing,
performed on cryopreserved blood collected at age 50 or 60, was used to
predict metastasis at 15- to 20-yr follow-up. In the subset of men with
modestly elevated PSA, a pre-specified model based on a panel of 4 KLK markers
increased the predictive discrimination of developing clinically diagnosable
prostate cancer. Among men with modestly elevated PSA at age 50 or 60, the
authors claim the 4 KLK (4Kscore assay) panel yielded C-indexes from 0.82 to
0.88 for the prediction of documented distant metastasis. The authors conclude
that screening at ages 50-60 years should focus on men with PSA in the top
quartile, and use the kallikrein panel to aid biopsy decision making.  
  
Despite the claims offered by these authors, there are many concerns. The
discussion alludes to the fact that if patients were selected by PSA of 4 or
above, or selecting age adjusted PSA cut-offs for biopsy, the number of
biopsies excluded would be similar but more advanced cancer would be missed.
This data is statistically modeled and hypothetical, and generated in a group
of patients biopsied under techniques not practiced today. Furthermore, the
authors chose a 5 year end point for supposedly missed clinically diagnosable
prostate cancer. However, the curves rise significantly after 5 years to
potentially unacceptable levels (almost 4% of the population at 10 years).  
  
Assay validation should be specific to the intended use population and
intended use. Although the Vickers study included patients with elevated PSA
in their training and validation study, the assay validation was not specific
to identifying men at risk for developing clinically diagnosable prostate
cancer at 5 years (an unacceptably short endpoint).  
  
The most recent data presented in the Parekh study3 has a number of flaws.

  1. This study includes men with PSA levels >10 ng/mL who may have increased risk of cancer and may require biopsy.
  2. This subgroup (PSA levels >10 ng/mL) is not separately modelled to determine if modeling adds benefit.
  3. The importance of total PSA and its fractions are obvious in the latest iteration of the 4K model. The AUC of the full model is 0.821, and without the incorporation of the hK2 the AUC is 0.806 with overlapping confidence intervals. This suggest that hK2 in the model/algorithm adds little. Its significance is unknown.
  4. The AUC of this model with total PSA should have been reported, as well as, reports of the stepwise addition of the other measurements to determine how the markers perform relative to total PSA. Confidence intervals should have been reported to determine overlap, as well as, comparison with an updated prostate cancer risk calculator, such as Rotterdam Prostate Cancer Risk Calculator.
  5. The clinical characteristics of the patients are very poorly defined - men in need of biopsy - yet the model includes men with prior negative biopsies.

  
In a retrospective study by Bryant et al,4 involving cryopreserved blood from
>6000 men in a large randomized prospective clinical trial involving
contemporary extended 10-coare biopsies, the 4 kallikrein panel was used to
demonstrate prediction improvement of biopsy outcomes compared with total PSA
and age. Because the previous statistical models were based on the kallikrein
levels measured in serum for previously unscreened men undergoing sextant
prostate biopsy, and because levels of some of the kallikrein markers differ
in plasma vs serum, new prediction models were generated in this study and
reported new AUCs. The authors also used decision curve analysis to
investigate whether the models could reduce the number of men undergoing
biopsy without delaying the diagnosis of high-grade disease in many men. They
claim that using a 6% risk of high-grade cancer as an illustrative cutoff, for
1000 biopsied men with PSA levels of 3.0 ng/mL or higher, the model would
reduce the need for biopsy in 428 men, detect 119 high-grade cancers, and
delay diagnosis of 14 of 133 high-grade cancers. They claim the 4 kallikrein
assay can predict the result of the prostate biopsy, and differentially detect
high-grade disease. However, the new AUC confidence levels of the model with
or without hK2 overlap, and men with PSA = 10 ng/mL were included.
Furthermore, the model used total PSA and free PSA (did not use intact PSA)
with a free to total PSA ratio. These components can easily be calculated, and
require no need for expensive testing.  
  
The Bryant study highlights a turning point with the development of a new
model/algorithm in response to changes in biopsy and grading practices, and
was subsequently locked down and applied to the Swedish community study, the
Stattin long-term follow-up study, and the Parekh validation study.
Furthermore, the Bryant authors have not proven the validation of the assay,
and admit their findings need to be confirmed in prospective research using
clinical cohorts.  
  
Finally, Konety et al,5 is marketed as a prospective decision impact study. In
this study, 611 patients seen by 35 academic and community urologists in the
US ordered the 4Kscore tests as part of their assessment of men referred for
abnormal PSA and/or digital rectal exam (DRE). The authors report that the
"results for the patients were stratified into low risk (< 7.5%), intermediate
risk (7.5%-19.9%), and high risk (20%) for aggressive prostate cancer. The
4Kscore Test results influenced biopsy decisions in 88.7% of the men.
Performing the 4Kscore Test resulted in a 64.6% reduction in prostate
biopsies in patients; the actual percentage of cases not proceeding to biopsy
were 94.0%, 52.9%, and 19.0% for men who had low-, intermediate-, and high-
risk 4Kscore Test results, respectively. A higher 4Kscore Test was
associated with greater likelihood of having a prostate biopsy (p < 0.001).
Among the 171 patients who had a biopsy, the 4Kscore risk category is
strongly associated with biopsy pathology. The 4Kscore Test, as a follow-up
test for an abnormal PSA and/or DRE results, significantly influenced the
physician and patient shared decision in clinical practice, which led to a
reduction in prostate biopsies while increasing the probability of detecting
aggressive cancer.  
  
The Konety study, although marketed as a prospective study, is not a
prospective study. A prospective clinical utility study requires prospective
enrollment of patients, treatment according to a defined pathway, using the
test result as an integral part of the care plan, and must demonstrate
statistically and clinically significant improvement in healthcare outcomes
versus the currently accepted standard of care by contemporary controls.
However, in the methods section of this article, the authors specify that the
study was "retrospective", and "no restrictions were placed on the urologists
in deciding which patients received the 4Kscore test or in making decisions
with the patient about whether to proceed with prostate biopsy".5 At best,
this study represents a retrospective observational study or survey.  
  
Finally, there is this assumption that missing an National Comprehensive
Cancer Network (NCCN) low risk patient will cause no harm. The only data for
this is in men following biopsy documentation and subsequent active
surveillance (AS). There is no evidence that observing a man with undiagnosed
low risk prostate cancer and projected longevity would not suffer harm. There
are no recommendations on suggested follow up if the 4Kscore suggests no
indication for biopsy. There is an unproven statement that serial PSA will
identify patients who may evolve and capture the missed high risk patients.
Independent evidence suggests the main indication for cessation of AS is not
PSA progression, but a worsening repeat biopsy.  
  
In summary, the intended use population has been inadequately validated; the
4Kscore model has continuously changed; the model has been recurrently tested
on potentially inappropriate patients (PSA > 10 ng/mL) and patients with
inadequate biopsy sampling; it is unclear how much the hK2 and possibly intact
PSA contribute to the model; the value of the 4Kscore model/algorithm is
fraught with statistical hypothesis and not prospective outcomes or
concordance in a defined patient population likely to be considered for biopsy
(e.g., PSA 3-10 ng/mL); assumptions are made that no harm will come to
following young men with unknown low grade prostate cancer (not on AS); there
is significant difficulty equating the model used in the Swedish study to the
presently proposed formula; and the incidence of clinically diagnosable
prostate cancer in patients with low risk by the model/algorithm at 10 years
is very concerning.  
  
Consequently, due to significant issues with assay validation and absence of
clinical utility, 4Kscore testing is not reasonable and necessary and is not
covered by Medicare.