Discussion
Searching the Gray Literature (for this horizon scan): LexisNexis,
CHI vs. Others
For our project, the meaning of gray literature evolved into referring to "any
literature which is not peer reviewed." However, given the broad definitions
for key terms such as "gray literature," "genetic test,"
"biomarker," and "in
development," one of the early challenges of this project was to identify
gray literature which was appropriate and applicable to our particular task
order. To this end, we found little precedent or guidance for systematic searching
of the gray literature for the purpose of a horizon scan in genetic testing
for cancer.
In the NLM's Etext on Health Technology Assessment Information resources,
finding the gray literature is demonstrated through the HTA example, which
starts with the HTA Database.5
We began our search with the NLM report
and continued to add gray literature resources to this list as our project
evolved. We carefully documented our methods in searching the gray literature
for this project because we believe that our report may serve as a novel yet
useful example of how to perform a gray literature search for a horizon scan
project. After rigorous exploration of numerous databases and resources, we
were able to identify a handful of gray literature sources that could be loosely
categorized into three different categories of utility for our project: high
utility, low to moderate utility, and not applicable.
For the purposes of our horizon scan, we found that the LexisNexis and CHI
databases to have the greatest utility for finding cancer genetic tests of
interest to our project. One final caveat, our particular method for searching
the gray literature is not meant to be definitive or apply universally to all
projects. Instead, our report is meant to provide one example of how the gray
literature can be searched for the purposes of a horizon scan on diagnostic
genetic tests in clinical development for cancer.
Genetic tests for cancer
Part I: Current genetic tests
In both parts of this project, we started our search with the same approach
of reviewing the scientific and gray literature while also attending scientific
conferences and interviewing expert opinions. In order to accomplish the first
goal of identifying genetic tests currently available for cancer care, we found
the commercial literature and Web sites for the largest diagnostic test companies
to be the most useful for addressing the first part of this project. We found
62 genetic tests for 9 different cancers. Given the broad definition for genetic
test that we used, it should not be a surprise that we found such a wide range
of genetic tests available, from basic protein biomarkers like AFP, to the
new multi-gene assay, Oncotype Dx, for predicting disease recurrence in breast
cancer. The compilation of one-page summaries provides more detailed information
on each genetic test currently available in the database. In addition, each
summary contains a brief synopsis of different search strategies and the amount
of literature that may be indicative of the amount of time and effort that
would be needed to focus on potential projects such as a systematic review
of the clinical validity and utility studies for an individual genetic test.
Part II: Genetic tests in development
One of the challenges that we encountered during this second part of the project
was trying to determine what genetic test was appropriate for being "in
clinical development" for cancer. Earlier, we discussed the five different
phases of development that a genetic test or biomarker must achieve in order
to eventually gain clinical acceptance (Figure 1). The evaluation and testing
of a diagnostic test can be a long and time consuming process; therefore, a
horizon scan for genetic tests in development may only be interested in tests
that are emerging from later phases of clinical development (phases 2–5)
in order to identify tests with the greater likelihood of having more immediate
clinical impact.
The next challenge we faced was to then find the most efficient resources
and databases that would identify genetic tests in development relevant to
our project. As we gained experience with the scientific literature, gray literature,
and professional meetings and interviews, we discovered that MEDLINE searches
were useful for finding information of pre-clinical exploratory biomarker and
genetic tests. However, we also found that MEDLINE and other databases that
search the scientific literature were not as efficient in identifying genetic
tests in the later phases of development. Instead, the gray literature, and
in particular LexisNexis and CHI, were the most useful in identifying genetic
tests in development and with more immediate commercial potential. The results
for Part II of this project can be found in Database III, which is a compilation
of genetic tests identified through various gray literature resources and expert
interviews.
Finally, we found 104 genetic tests in development through our systematic
search of the gray literature and other sources. We discovered that the LexisNexis
and CHI resources had the highest utility for identifying genetic tests in
development that may have more immediate commercial impact. However, we are
aware that despite all our efforts, these lists are not necessarily comprehensive
and that it is possible that a handful of promising genetic tests for cancer
exist but do not appear in our database. Perhaps, this is to be expected since
we are entering a time of unprecedented growth for the medical diagnostic industry
as physicians, patients, and society are just beginning to benefit from the
fruits of labor stemming from the completion of the Human Genome Project in
2003.
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