Page 2 - The Contemporary Role of Conventional Imaging for Staging, Re-staging, and Monitoring Prostate Cancer: Impact on Management

continued from cover page
MRI or CT results with pathologic findings from lymph
node dissection, which is a gold standard, provide the
clinician with a good understanding of the imaging
modality’s performance. However, imaging studies
that examine detection rates without a gold standard
comparator or clinical impact, provide indirect
information about the test’s ability to reflect the true
state of the disease or the need for management
change. Also, imaging studies may report the accuracy
of the modality on a per-patient or per-lesion basis.
In prostate cancer staging, per-patient accuracy is the
most relevant parameter.
It is noteworthy that the performance of a specific
imaging modality changes in different clinical
scenarios, and as a result, the use of imaging
procedures may vary along the prostate cancer disease
continuum. The sensitivity and specificity of an
imaging procedure must be considered in the context
of the available treatment options and their clinical
implications; the margin of error associated with a
particular modality should be weighed into treatment
decisions.
As prostate cancer management evolves, clinical
practice will need newer imaging modalities. At
the present time, however, there is little evidence
to demonstrate that the increased sensitivity of
an imaging technique alters the rate of disease
progression or overall survival. Current guidelines
consider the available imaging evidence in relation to
the prostate cancer treatment algorithm and aim to
direct appropriate use of imaging resources to optimize
patient outcomes.
Accuracy: the ability of a test to discriminate between
the presence and the absence of a disease
[TP + TN/all cases].
Sensitivity: the proportion of people with the disease
who will have a positive result [TP/(TP + FN)]. A test
with high sensitivity is useful for ruling out a condition
if the test is negative.
Specificity: the proportion of people without the
disease who will have a negative result [TN/(TN+FP)].
A test with a high specificity is useful for ruling in the
condition of interest if the test is positive.
FN = false negative; FP = false positive; TN = true negative;
TP = true positive.
2
Primary Staging Before
Local Therapies
he accuracy of initial staging of prostate cancer
Tis critical for determining an optimal treatment
plan. Imaging in this setting plays a role in local
staging and determining lymph node and bone
metastases. In the SEER 18 (2007-2013) dataset, 12%
of men with newly diagnosed prostate cancer had
regional lymph node involvement and 5% had distant
metastases at presentation (79% of prostate cancers
were confined to the primary site, 4% were unstaged).
1
During primary staging, imaging resources should be
targeted to the men most at risk for advanced disease;
bone scintigraphy and CT scans are unlikely to add
information that influences the management plan in
patients with favourable risk.
Detecting Lymph Node Metastases
RI and CT depict morphologic characteristics such
Mas the size and shape of the lymph nodes, and
often fail to detect small metastases in lymph nodes
that are normal in size and appearance. The accuracy
of these modalities has been determined through
several studies that have used lymph node dissection,
an ideal comparator.
In one study, MRI results were correlated with
histopathologic findings in patients with presurgical,
early stage prostate cancer undergoing surgical
lymph node resection or biopsy. MRI for lymph node
metastasis had a sensitivity of 45.4%, a specificity of
78.7%, and accuracy of 65%. 2
In a meta-analysis of 24 studies, the accuracy of CT and
MRI in the staging of pelvic lymph nodes in patients
with prostate cancer was evaluated. Pooled sensitivity
was 42% for CT and 39% for MRI. Pooled specificity
was 82% with each of these modalities. The authors
concluded that CT and MRI demonstrated equally poor
performance and misrepresented the patient’s true
status regarding nodal metastases. 3
Detecting Bone Metastases
one scan using technetium methylene
Bdiphosphonate (Tc 99m MDP) is the most
frequently used imaging method to detect prostate
cancer bone metastases. Bone biopsy is not a practical
comparator in bone imaging studies, and this may
explain the difficulty of assessing true sensitivity and
specificity of bone scan, MRI, and CT in this setting.
Early studies examined bone metastasis detection rates
and provided guidance regarding which patients were
likely to benefit from imaging investigations.