SAN ANTONIO – The Clinical Treatment Score post 5 years (CTS5) has been validated for the prediction of late distant recurrences in a large contemporary cohort of breast cancer patients drawn from the landmark TAILORx study – but only provided they’re over age 50 at the time of their initial breast cancer diagnosis, Ivana Sestak, PhD, reported at the San Antonio Breast Cancer Symposium.
Bruce Jancin/MDedge News
Dr. Ivana Sestak
“The CTS5 was much less prognostic in younger patients, and we did not observe good discrimination for the CTS5 in this cohort,” she said. “Further evaluation in premenopausal cohorts is needed before CTS5 can be applied to younger patients.”
She and her coworkers developed the CTS5 as a simple, expeditious tool to identify women at high risk of late distance recurrence of estrogen receptor–positive breast cancer after successfully completing 5 years of endocrine therapy. It’s designed to serve as an aid to physicians and patients in clinical decision making: Women who are CTS5 high risk are likely to benefit from extended endocrine therapy beyond the 5-year mark, while those at low risk are not.
“Trials so far have shown only a modest risk reduction of around 5% with extended endocrine therapy. This may be partly due to the fact that none of these trials had specifically selected patients who were at high risk of developing a late recurrence. It is therefore crucial that we identify those patients who are at high risk of late recurrence, as they will benefit most from extended endocrine therapy,” explained Dr. Sestak, a medical statistician at Queen Mary University, London.
The CTS5 calculator is freely available online at www.cts5-calculator.com. Clinicians simply plug in readily available information on four specific variables for their patients who have completed 5 years of endocrine therapy free of distant recurrence: age at breast cancer diagnosis, tumor size in millimeters, tumor grade, and number of involved nodes. The calculator promptly spits out a CTS5 score and the associated risk of distant recurrence during years 5-10 after initial diagnosis. That risk is categorized as low if it’s 5% or less in years 5-10, and high if it’s greater than 10%.
The CTS5 was developed and validated using long-term follow-up data on more than 11,000 postmenopausal breast cancer patients in the ATAC and BIG1-98 randomized trials. The CTS5 performed well in those tests. But those studies were completed more than a decade ago and were limited to postmenopausal patients. Dr. Sestak and coinvestigators wanted to assess the tool’s discriminatory powers in a contemporary population of breast cancer patients that included large numbers of premenopausal women. So they tapped into the National Cancer Institute–sponsored TAILORx study, which included 7,353 breast cancer patients who were distant recurrence free after 5 years. All had early-stage, hormone receptor–positive, HER2-negative, and axillary node–negative breast cancer. And all underwent baseline testing using Genomic Health’s Oncotype DX Breast Recurrence Score to assess expression of 21 genes associated with breast cancer recurrence.
The CTS5 proved to be highly prognostic in the overall TAILORx population. But upon drilling down further, Dr. Sestak and coworkers determined that CTS5 had only marginal prognostic value in the 2,259 women age 50 years or younger. Indeed, not a single patient in that age group was categorized as CTS5 high risk, and the actual distant recurrence rates during years 5-9 weren’t significantly different between the low- and intermediate-risk CTS5 groups.
In contrast, CTS5 performed well as a prognosticator in the 2,257 TAILORx participants over age 50 who received both chemotherapy and endocrine therapy during their first 5 years following diagnosis. For a fast and simple test with zero cost, it displayed impressive discriminatory power: The 63.8% of women classified as CTS5 low risk had a 2.6% distant recurrence rate – and thus constituted a group who could reasonably avoid extended endocrine therapy – while the 3.5% who were CTS5 high risk had a 9.5% event rate, and the intermediate-risk group had a 7.3% event rate. The prognostic power of CTS5 in the 2,837 women aged over 50 years who received only hormonal therapy was less robust, albeit still statistically significant.
In women classified as being at low risk of recurrence based upon an Oncotype DX score of 0-10, the CTS5 was not a significant prognosticator for the prediction of late distant recurrences. However, in those who were at intermediate or high risk as determined by a score of 11-100 on the Oncotype test, CTS5 was highly prognostic.
A significant limitation of this CTS5 validation study in the TAILORx population was that only a median 2.86 years of follow-up data after the 5-year mark was available – not sufficient time for a large number of distant recurrences. The rate was 3.1% in women treated with only endocrine therapy who had an Oncotype DX score of 0-25, and 3.8% in those with a score of 11-100 who received both chemotherapy and endocrine therapy.
Dr. Sestak shrugged off the less than stellar performance of the CTS5 in women aged age 50 years or younger in the TAILORx analysis.
“We developed the CTS5 specifically in postmenopausal women, so we’re not really surprised that it’s less prognostic in young women,” she said.
Her group next plans to evaluate the CTS5 in another large premenopausal cohort of breast cancer patients.
“If it’s not prognostic there, then we’ll have to adjust the algorithm and recalibrate it specifically for younger patients,” according to Dr. Sestak.
The TAILORx validation study was supported by Breast Cancer Now, Cancer Research UK, Exact Sciences, and the University of London. Dr. Sestak reported having received honoraria from Myriad Genetics, Nanostring Technology, and Pfizer Oncology.
SOURCE: Sestak I et al. SABCS 2019, Abstract GS4-03.