Comparing breast biomarker status between routine immunohistochemistry and FISH studies and Oncotype DX testing, a study of 610 cases.

Introduction: Oncotype DX (ODX) testing uses reverse transcription polymerase chain reaction (RT-PCR) to predict distant recurrence rate of estrogen receptor positive (ER+)/HER2-negative (HER2-)/lymph node-negative (LN-) breast cancers. ODX also reports the status of breast cancer biomarkers, ER, progesterone receptor (PR), and HER2. This study examined the discrepancy rate of breast cancer biomarker status as reported by ODX vs routinely used immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) methods.

Methods: A total of 610 breast cancer cases (609 ER+ and 1 ER-negative (ER-) by IHC) with ODX reports were reviewed. ER, PR, and HER2 status from ODX reports were compared with results from IHC and FISH studies.

Results: There was an overall high concordance rate between IHC and ODX for ER expression (603/610 concordant, 98.9%) and moderate concordance for PR expression (549/610 concordant, 90%). Of the seven ER-discrepant cases, six were positive by IHC but negative by ODX. Of the 61 PR-discrepant cases, 41 were positive by IHC but negative by ODX. Of the 610 cases, 568 had HER2 results reported by ODX. Five cases were HER2+ by IHC/FISH (0.88%). One of these five cases was reported as HER2+, two as HER2-, and two as HER2-equivocal by ODX. None of the cases that were HER2- or equivocal by IHC/FISH was reported as HER2+ by ODX.

Conclusions: There is good concordance between IHC and ODX for ER and PR expression, but IHC is more sensitive. The significant discordance in HER2+ cases may discourage reporting HER2 status by ODX testing.