Two Genomic Tests for Breast Cancer Recurrence Compared

Zosia Chustecka

May 05, 2011

May 5, 2011 — Several genomic tests for use in breast cancer are now available, but how they compare and relate to one another remains a "clinical challenge for practicing physicians," according to a researcher who set out to evaluate 2 of these products in the same patients.

Dr. Catherine Kelly

"This is the first study to compare 2 standardized, readily available but conceptually different prognostic risk predictors," said Catherine Kelly, MD, from the Mater Misericordiae University Hospital, Dublin, Ireland.

The trial compared the widely used Oncotype DX test with the recently launched PAM50 test in a cohort of 119 breast cancer patients.

Presenting the results today at the IMPAKT Breast Cancer Conference in Brussels, Belgium, she said: "The results indicate that there is reasonably good agreement between the 2 methods for high and low prognostic risk assignment."

However, the intermediate-risk groups showed discordant results. About half of the patients who were categorized as intermediate risk by the Oncotype DX test were categorized as low risk by the PAM50 test.

This could save some women from undergoing chemotherapy, noted another expert. Speaking during a press briefing, Nadia Harbeck, MD, from the University of Cologne, Germany, who is executive chair of IMPAKT 2011, said that the intermediate-risk result from the Oncotype DX test "makes us feel insecure."

Clinicians use the Oncotype DX test to help them decide on treatment, she explained. When the test identifies a women as being at high risk for breast cancer recurrence, it is recommended that she undergo both chemotherapy and endocrine therapy; a low-risk result leads to treatment with endocrine therapy only. The intermediate-risk result presents a dilemma.

"Personally, I would rather treat than not treat these women, if they want maximum security from their breast cancer," Dr. Harbeck said.

However, these new results suggest that the second test, PAM50, could recategorize this intermediate group and identify women who are at low risk. "Maybe there is a role for combining these tests," she said. "They may complement one another."

Dr. Kelly cautioned, however, that there are no outcome data as yet, and that the PAM50 test has only recently been launched and is still undergoing validation.

"This new test potentially adds information, and this is interesting and potentially useful information, but we don't have outcome data," she emphasized. "Outcome data are required to show which test is getting it right."

Patients Who Present a Quandary

The study was conducted in breast cancer patients who would present a quandary for clinicians considering adjuvant therapy after surgery. All of the 119 patients were classified by researchers as having a "clinically intermediate" risk for recurrence on the basis of several criteria: a median tumor size of 1.5 cm; and estrogen-receptor-positive, HER2-negative, lymph-node-negative disease, most of which was grade 2.

"In other words, these patients would likely be a challenge in terms of whether they would benefit from chemotherapy or not," Dr. Kelly explained.

"In these situations, multigene assays can provide additional independent prognostic information," she added. Both tests were used on samples taken from all women (and were both conducted on paraffin-embedded tissue).

Oncotype DX measures the activity of 21 genes and generates a recurrence score that categorizes women into high-, intermediate-, and low-risk groups, depending on the risk for distant metastases.

PAM50 measures the activity of 50 genes and stratifies breast cancer into 5 subtypes: luminal A, luminal B, basal-like, HER2-enriched, and normal-like. The luminal A subtype is considered to be low risk for recurrence, and patients with this subtype and negative lymph nodes can forego chemotherapy, Dr. Kelly explained. In comparison, the luminal B subtype is at higher risk for recurrence, she added.

The results from the study showed that all patients who were categorized as high risk by the Oncotype DX test were categorized as the luminal B or basal-like subtype by the PAM50 test (both considered to be higher risk).

In addition, the majority of patients (83%) who were categorized as low risk by Oncotype DX were categorized as the luminal A subtype (low risk) by the PAM50 test.

However, half of the patients (51%) who were categorized as intermediate risk by Oncotype DX were categorized as the low-risk luminal A subtype on the PAM50 test.

There was other discordance between the tests. Not all of the cancers that were categorized by PAM50 as being of the luminal A subtype (hence, low risk) were categorized as low risk by Oncotype DX; this test determined that 70% were low risk but 30% were intermediate risk.

Commenting on the study, which he was not involved in, Roberto Labianca, MD, from the Ospedali Riuniti de Bergamo, Italy, said: "The data with PAM50 are very interesting, because they indicate that in the intermediate-risk group (as defined by the well-established Oncotype DX test), it is possible to exclude additional patients from adjuvant chemotherapy."

"However, a validation of these findings in a larger population is mandatory before they can be translated into clinical practice," he added.

IMPAKT Breast Cancer Conference: Abstract 82O. Presented May 5, 2011.


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