A Prospective Cohort Study Evaluating Risk of Local Recurrence Following Breast Conserving Surgery and Endocrine Therapy in Low Risk Luminal A Breast Cancer
The independent prognostic ability of the luminal A subtype has been demonstrated in two
retrospective analyses of prospective trials and suggests that luminal A combined with other
known clinical prognostic factors could be used to select patients treated with BCS at very
low risk for IBTR who could avoid BI. Given that using intrinsic subtyping combined with
other clinical factors to identify women who could avoid BI would be a major change in
clinical practice, we propose that a prospective study is necessary to confirm that such an
approach can accurately identify a group of women at very low risk for IBTR following BCS.
We anticipate that the risk of IBTR in the low risk group is likely to be lower than that
observed in previous trials (predicted to be < 5% at 5 years and < 10% at 10 years) for
several reasons: first, our selection criteria (node negative, luminal A, > or = 60 years,
tumours < or = 2cm, excision margin > or = 2mm post-BCS, absence of lobular cancers,
extensive intraductal component and lymphovascular invasion) are more restrictive than in
previous trials and second, the risks of IBTR are steadily decreasing over time due to
improvements in mammographic screening, pre-op staging, tumour localization, and surgical
practice. The expected low failure rates are unlikely to warrant the use of radiation.
A prospective cohort study was identified as the most appropriate and efficient design as
our primary hypothesis is that a group of patients at very low risk of IBTR can be
identified. A randomized trial could address the effectiveness of radiation in such a cohort
of patients, but would require a much larger sample size to detect very small differences,
which would not be clinically meaningful. During the conduct of this trial it is anticipated
that patients who do not meet study criteria or who decline study enrollment, will continue
to receive BI after BCS.
Observational Model: Cohort, Time Perspective: Prospective
Ipsilateral Breast Tumour Recurrence (IBTR)
The primary outcome is IBTR defined as recurrent invasive or in-situ cancer in the ipsilateral breast during follow-up. Histological evidence of recurrence will be required. All recurrences will be reviewed by a central adjudication committee.
Tim Whelan, MD
Ontario Clinical Oncology Group (OCOG)
Canada: Health Canada