Abstract
Background:
The ICON6 trial (ISRCTN68510403) is a phase III academic-led, international,
randomized, three-arm, double-blind, placebo-controlled trial of the
addition of cediranib to chemotherapy in recurrent ovarian cancer. It
investigated the use of placebo during chemotherapy and maintenance (arm A),
cediranib alongside chemotherapy followed by placebo maintenance (arm B) and
cediranib throughout both periods (arm C). Results of the primary comparison
showed a meaningful gain in progression-free survival (time to progression
or death from any cause) when comparing arm A (placebo) with arm C
(cediranib). As a consequence of the positive results, AstraZeneca was
engaged with the Medical Research Council trials unit to discuss regulatory
submission using ICON6 as the single pivotal trial.
Methods:
A relatively limited level of on-site monitoring, single data entry and
investigator’s local evaluation of progression were used on trial. In order
to submit a license application, it was decided that (a) extensive
retrospective source data verification of medical records against case
report forms should be performed, (b) further quality control checks for
accuracy of data entry should be performed and (c) blinded independent
central review of images used to define progression should be undertaken. To
assess the value of these extra activities, we summarize the impact on both
efficacy and safety outcomes.
Results:
Data point changes were minimal; those key to the primary results had a 0.47%
error rate (36/7686), and supporting data points had a 0.18% error rate
(109/59,261). The impact of the source data verification and quality control
processes were analyzed jointly. The conclusion drawn for the primary
outcome measure of progression-free survival between arm A and arm C was
unchanged. The log-rank test p-value changed only at the sixth decimal
place, the hazard ratio does not change from 0.57 with the exception of a
marginal change in its upper bound (0.74–0.73) and the median
progression-free survival benefit from arm C remained at 2.4 months.
Separately, the blinded independent central review of progression scans was
performed as a sensitivity analysis. Estimates and p values varied slightly
but overall demonstrated a difference in arms, which is consistent with the
initial result. Some increases in toxicity were observed, though these were
generally minor, with the exception of hypertension. However, none of these
increases were systematically biased toward one arm.
Conclusion:
The conduct of this pragmatic, academic-sponsored trial was sufficient given
the robustness of the results, shown by the results remaining largely
unchanged following retrospective verification despite not being designed
for use in a marketing authorization. The burden of such comprehensive
retrospective effort required to ensure the results of ICON6 were acceptable
to regulators is difficult to justify.
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