Cancer is a disease that affects millions of individuals around
the world annually.
71% of cancer deaths occur from cancers that are not
routinely screened for.
While the vast majority of cancers don't show
any symptoms until later stages.
A late diagnosis drastically affects
the patient's survival rates,
treatment options, and treatment outcomes.
Cancer detection include non-invasive imaging tests and invasive procedures
such as a biopsy. These procedures are time-consuming and often
associated with an increase in personal and economic burden.
Currently,
five main cancer types,
have been identified for routine screening.
These include breast, cervical,
colorectal,
prostate, and in high-risk individuals, lung cancer.
Studies have been conducted on alternative screening tests and one
such test that is emerging with promising results is the Galleri test.
The Galleri test is a multi-cancer
early detection test
abbreviated as MCED and it's developed by the company GRAIL.
The presence
of cancer is detected by this test
by looking at
genomic signals present in the blood.
If a cancer signal is detected,
the results can indicate where in the body the cancer
signal is coming from. Following this finding,
your healthcare provider will be able to recommend next steps,
often involving further cancer screening
through Imaging tests and biopsies. This test currently
detects 52 types
of cancers in the human body through a
simple blood test.
So you may be wondering,
how a simple blood test is able to detect cancer?
All cells, healthy
and cancer,
shed DNA into the bloodstream.
The DNA shed from cancer and non-cancerous cells looks different
under the microscope.
Therefore, blood is a suitable sample for detecting
cancer biomarkers
as it contains circulating tumour cells and
tumour cell-free DNA,
also known as cfDNA.
The Galleri test uses
next-generation sequencing and a targeted methylation-based assay coupled
with machine learning to analyze methylation patterns of cfDNA in the bloodstream.
cfDNA carries cancer-specific signals
in its methylation patterns, due to which, certain DNA methylation patterns can serve
as cancer signals. These signals can be distinguished from background genomic signals
of healthy cfDNA and possibly provide information about
the origin of the signal at the time
the blood was drawn.
In an individual with cancer, abnormal
methylation patterns and the resulting changes in gene expression
can contribute to tumour growth.
Different cancers shed
DNA into the bloodstream
a different rates.
The likelihood of cancer being
detected by the Galleri test increases with the proportion
of cfDNA in a blood sample.
In the majority of cancer types, the detectability increases with cancer stage
as the proportion of cfDNA in the bloodstream also increases with the cancer stage.
However, there are some cancers
that shed more DNA at earlier stages
and are therefore associated with
higher mortality rates.
Results are received in approximately two weeks
following the blood draw and should be interpreted and communicated
to you by your healthcare provider
in the context of your medical history,
clinical signs, and symptoms.
The result can be negative,
meaning that cancer signals were not detected or positive, meaning
that cancer signals were detected.
A positive result requires further cancer screening
through diagnostic and invasive medical procedures such as imaging
and biopsies to confirm the cancer diagnosis.
A negative result does not rule out cancer and
is only an interpretation of the fact that the test
was unable to detect cancer DNA signals in the blood,
suggesting that cancer is not present
or
the cancer could be located in different part of the body
or the testing is insufficient to detect cancer. Further investigations
following a positive or negative results are conducted to the
discretion of your healthcare provider in response to your
medical history and current health.
The results could also be false positive,
meaning that cancer signal was detected when cancer is not present
or false negative,
meaning that cancer signal was not detected when cancer is present
As per a few studies involving
the Galleri test,
the test has a false positive rate of 0.7%.
Although the Galleri test has promising results,
it brings with it
a few limitations.
The Galleri test does not detect all cancers and should
be used in addition to routine cancer screening test
recommended by
healthcare providers.
Despite a negative result, the test does not measure
your genetic risk for developing cancer in the future.
Therefore,
it is important to continue with routine cancer screening that
your healthcare provider recommends.
Even with its revolutionary benefits in the context of
early cancer detection,
the Galleri test has not yet been cleared or approved
by the Food and Drug Administration.
The Galleri test is recommended for use in adults with
an elevated risk of cancer,
individuals aged 50 and older, and individuals experiencing cancer symptoms.
On the other hand, the Galleri test is not
recommended for use in pregnant individuals,
individuals aged 21 and younger, and individuals undergoing active cancer
treatment.
If you fit the eligibility criteria, the next step
would be to discuss it with your healthcare provider.
Some questions that you could ask your health care
provider are:
Do I have an increased risk for cancer?
What cancer screening tests are recommended for me?
Am I up-to-date
on cancer screening tests
that are appropriate for me?
For cancers that do not have cancer
screening tests,
how are they detected today?
And is the Galleri MCED test right for me?
Currently, the Galleri test
is available via prescription only. While the cost of
the Galleri test is listed as $949 USD.
The prices may vary from region to region,
as well as depending on the healthcare provider or
clinic ordering the test.
It is currently not covered by insurance and therefore,
the only payment plans include variations of self-pay.
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