(ChemotherapyAdvisor) – Use of the Mammostrat panel predicted distant relapse-free survival (DRFS) in postmenopausal women with hormone-sensitive early breast cancer treated with exemestane and tamoxifen followed by exemestane regardless of nodal status and chemotherapy, a study in the Journal of Clinical Oncology online October 8 has found.

“Although endocrine therapy is an effective adjuvant treatment for patients with estrogen receptor (ER)–expressing (ER-positive) early breast cancer, a critical evaluation of adjuvant trials of tamoxifen suggested many patients are not cured after this therapy,” noted John M.S. Bartlett, PhD, Ontario Institute for Cancer Research, Toronto, Ontario, Canada. “The challenge is to prospectively identify such patients,” he added, in explaining the rationale for the largest evaluation of the Mammostrat prognostic panel to date.

The efficacy of Mammostrat, which uses five immunohistochemical (IHC) markers to stratify patients regarding recurrence risk, was evaluated in the Tamoxifen versus Exemestane Adjuvant Multicenter (TEAM) trial; 47% of patients were node-positive and 36% had been treated with adjuvant chemotherapy.

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After collecting pathology blocks from 4,598 TEAM patients, they constructed tissue microarrays, which were stained and assessed for positivity for p53, HTF9C, CEACAM5, NDRG1, and SLC7A5, and then analyzed DRFS and disease-free survival based on the assigned Mammostrat risk score.

“Mammostrat provided significant additional information on DRFS after endocrine therapy in ER–positive node-negative patients (n=1,226) who did not receive chemotherapy (P=0.004),” they reported. “Additional analyses in all patients not exposed to chemotherapy, irrespective of nodal status (n=2,559) and in the entire cohort (n=3,837) showed Mammostrat scores provided additional information on DRFS in these groups (P=0.001 and P<0.001, respectively; multivariate analyses).” No differences were observed between the two endocrine treatment regimens.

“The ability of this test to provide additional outcome data after treatment provides additional evidence of its use in risk stratification of ER-positive postmenopausal patients with breast cancer,” the authors concluded.

An accompanying editorial noted, “until recently, oncologists struggled to determine prognosis and make chemotherapy decisions in patients with early-stage, ER-positive breast cancer. Now, with a plethora of tests to choose from, the dilemmas are which test to request and how to assimilate information from different tests.

“The future of diagnostic testing in ER-positive breast cancer likely will rely on devising and reliably deploying assays that predict for benefit of additional therapy such as newer targeted therapies. It is certain that no particular technology holds the key, and all possible avenues need to be explored. Indeed, we may need to go back to revisit IHC as we move toward the future.”