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Investigators Publish Three-Year Outcome Analysis From PlanB Study Using Oncotype DX

A correction has been made to the name of the group leading the PlanB study.

NEW YORK (GenomeWeb) – European investigators have published new outcomes results from the large PlanB study in which Genomic Health's Oncotype DX breast cancer test has been used to guide treatment for women with node-negative and node-positive breast cancer.

Published today in the Journal of Clinical Oncology, the results from the three-year outcomes analysis indicate that women in the trial with Oncotype DX recurrence scores of 11 or less had 98 percent disease-free survival rates even if traditional parameters would have defined them as high risk.

Led by the West German Study Group, PlanB was initiated in 2009 as a chemotherapy trial for comparing anthracycline-containing chemotherapy to anthracycline-free regimens.

Soon after its initiation, the trial was amended to recommend omission of chemotherapy in favor of hormonal therapy alone in patients with hormone receptor-positive disease with an Oncotype DX recurrence score (RS) under 12. Participants with intermediate and high scores — RS of 12 or higher — were randomized to different chemotherapy regimens. Between 2009 and 2011, the trial enrolled about 3,100 patients.

According to authors of the new outcome analysis, Oncotype DX results were available for a total of 2,568 locally hormone receptor-positive patients among this larger cohort. Of these, about 18 percent were classified as low risk, with an RS below 12, 60 percent as intermediate with an RS between 12 and 25, and 21 as high with an RS over 25.

Physicians omitted chemotherapy on the basis of a low RS for 348 patients — including 31 percent who were node-positive and 20 percent who had tumors rated grade-three based on immunohistochemistry analysis.

Studying patient outcomes after three years, the study group found that 98 percent of the low RS group was disease free at the three-year point despite the presence of other risk factors that would define them as high risk.

"Even with an only 3-year follow-up, such a high rate of DFS almost excludes possible benefit from adjuvant chemotherapy," the authors wrote.

The high RS group with scores over 25, meanwhile, had a lower three-year disease-free survival rate of 92 percent despite receiving adjuvant chemotherapy.

According to Genomic Health, the findings of the new PlanB analysis for women with low recurrence scores are consistent with results from another large prospective trial, TAILORx — published in the New England Journal of Medicine last year — which focused only on node-negative subjects.

The new results from PlanB also found that patients with RS results between 12 and 25 had similarly excellent outcomes, with disease-free survival of 98 percent at three years. The study, however, did not compare chemotherapy versus endocrine therapy alone in this intermediate group, so does not offer direct evidence of whether Oncotype DX can further stratify treatments for these patients.

The question of what an Oncotype DX intermediate RS indicates clinically has been a point of contention in the field for some time, and lack of clarity on how to treat intermediate RS patients is something competing labs have pointed to as a downside of Genomic Health's test.

Several prospective trials are currently investigating the benefit of added chemotherapy versus hormonal therapy alone in patients with intermediate RS, including TAILORx. Patients in the intermediate RS group in TAILORx have been doing so well, however that there haven't been enough recurrences or other events yet to complete an analysis.

Another prospective trial, RxPonder is also addressing the question of the utility of Oncotype DX in guiding therapeutic decision-making for intermediate-score patients.

Further, though the cutoff point used in both PlanB and TAILORx for the low RS group was an RS of 11, other studies have placed the cutoff point higher for what would be the intermediate group according these studies.

For example, Genomic Health presented data last year at the 2015 European Cancer Congress from a study by Israel's Clalit Health Services, which showed that women with Oncotype DX RS results of less than 18 — the majority of whom were treated with hormonal therapy alone — had excellent outcomes with less than a one percent chance of distant recurrence or breast cancer-specific mortality at five years.

The company has announced that more comprehensive five-year results from PlanB will also be highlighted in the official European Breast Cancer Conference later this month.