Breast Cancer Recurrence Score Assay has Uncertain Effect on Chemotherapy Use

Use of recurrence score assay lowers the likelihood of receiving chemotherapy in high-risk breast cancer patients, but raises it in women with low-risk disease

medwireNews: Uptake of the Oncotype DX 21-Gene recurrence score (RS) assay, which estimates the benefit of adjuvant chemotherapy in breast cancer patients, is not significantly associated with receipt of chemotherapy, but assay use does have a differential impact across risk subgroups, US researchers report.

Specifically, use of the assay is significantly associated with reduced chemotherapy use in high-risk patients and with increased chemotherapy use in patients with low-risk disease, compared with not using the assay.

The study authors used a Surveillance, Epidemiology, and End Results and Medicare linked dataset to identify 40,044 women aged 65 years or older with a diagnosis of Oestrogen receptor-positive, nonmetastatic, invasive breast cancer during a 5-year period following the introduction of the assay in 2004.

Multivariable analysis showed no significant association between overall assay use and chemotherapy receipt, but it did reveal a significant interaction between assay use and risk groups as defined by the US National Comprehensive Cancer Network guidelines.

Among the 24.6% of women with high-risk disease, RS assay use compared with no assay use was significantly associated with a decreased likelihood of undergoing chemotherapy, with an odds ratio of 0.36. By contrast, among the 24.0% of patients classified as low risk, the probability of receiving chemotherapy was a significant 3.71-fold higher in women who did than in those who did not undergo testing.

Age was the other factor significantly associated with chemotherapy use, in light of which the researchers restricted the analysis to women aged between 65 and 70 years, but the findings were similar to those in the overall cohort.

During the study period, the use of chemotherapy in the overall study cohort remained “relatively stable” at 14.3%, they report. But among women who underwent RS assay testing, chemotherapy use declined from 20.0% in 2005 to 14.6% in 2009.

Uptake of chemotherapy also decreased in the subgroup of women aged 70 years or younger, from 29.1% in 2005 to 24.0% in 2009. However, this decline appeared to be restricted to women with high-risk disease and those who received the RS assay.

The team, led by Michaela Dinan from Duke University School of Medicine in Durham, North Carolina, writes in JAMA Oncology: “In this observational analysis, we could not determine to what extent decreased chemotherapy use reflects the influence of RS assay adoption or unrelated changes in practice over the same period.”

In a related commentary, Allison Kurian, from Stanford University School of Medicine in California, USA, and Christopher Friese, from the University of Michigan School of Nursing in Ann Arbor, USA, commend the study authors on their population-based approach, but note that many critical details, such as data from women younger than 65 years of age and the results of the RS assay, as well as patient and physician perspectives, are “missing from this bird’s-eye view” thereby limiting the understanding of how RS assay use informs treatment decisions.

The commentators add that in light of the gaps in available data, “it is impossible to determine whether physicians followed RS guidance despite its discordance from standard tumor prognostic characteristics, or whether they chose to dismiss an RS assay result that was concordant with tumor features in favor of a different treatment path.”

And they conclude: “Research initiatives that integrate the breadth of cancer registries with the depth of physician and patient survey data can offer a window into the clinical encounter, along with an outward view of impact across the population.”

References

Dinan MA, Mi X, Reed SD, Lyman GH, Curtis LH. Association Between Use of the 21-Gene Recurrence Score Assay and Receipt of Chemotherapy Among Medicare Beneficiaries With Early-Stage Breast Cancer, 2005-2009. JAMA Oncol; Advance online publication 27 August 2015. doi:10.1001/jamaoncol.2015.2722

Kurian AW, Friese CR. Precision Medicine in Breast Cancer Care. An Early Glimpse of Impact? JAMA Oncol; Advance online publication 27 August 2015. doi:10.1001/jamaoncol.2015.2719

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