The Impact of 2013 Updated ASCO/CAP HER2 Guidelines on the Diagnosis and Management of Invasive Breast Cancer: A Single-Center Study of 1739 Cases

The impact of 2018 ASCO-CAP HER2 testing guidelines on breast cancer HER2 results. An audit of 2132 consecutive cases evaluated by immunohistochemistry and in situ hybridization

The 2018 iteration of the ASCO-CAP HER2 testing guidelines proposes significant changes with an emphasis on the integration of concurrent immunohistochemistry (IHC) and in situ hybridization (ISH). We wished to evaluate the impact of these changes on clinical practice. Between Jan 2012 to Feb 2017, 2132 consecutive invasive breast carcinomas were evaluated with IHC and ISH for HER2. The sample tested was the breast primary or axillary nodes in all but 57 (2.7%) distant metastases. For 1824 cases with both dual-probe ISH and IHC results, the ISH subgroup was 1: 299 (16.4%), 2: 19 (1.0%), 1.0%, 3: 6 (0.3%), 4: 48 (2.6%) and 5: 1452 (79.6%). Ultimately 21% of group 2 and 4 cases and 80% of group 4 cases were positive. The change in HER2 status between the 2018 vs 2013 was: amplified in 323 (15.2%) vs 15.5%; not amplified in 1804 (84.6%) vs 82.2%; equivocal in 0 vs 2.3% previously. In 22 of 2127 cases (1.03%) the 2013 and 2018 results were discordant, all in groups 2-4. The discrepant cases included 15 of 331 (4.5%) of 2013 amplified cancers, now negative (all in groups 2 or 3) and 7 of 1796 (0.4%) 2013 nonamplified cases, now positive (all in group 4). Because of routine testing with both IHC and ISH, we found 6 of 1147 (0.52%) IHC negative (0 or 1+) cases were amplified by ISH. Further, 19 of 289 (6.6%) of IHC 3+ cases were nonamplified by ISH, circumstances not covered by these guidelines. In summary at the population level, the 2018 ASCO-CAP guidelines have a 99% agreement with the 2013 results. A major advantage is the abolishment of the clinically problematic equivocal category. Routine performance of both IHC and ISH uncovers a small proportion of cancers whose HER2 status is not addressed by these guidelines.

Impact of 2013 ASCO/CAP guidelines on various HER2 reporting categories in breast cancer by fluorescentin-situhybridization and Immunohistochemistry: A meta-analysis with systematic review

Objective:

The ASCO/CAP guidelines for reporting HER2 in breast cancer, first released in 2007, aimed to standardize the reporting protocol, and were updated in 2013 and 2018, to ensure right treatment. Several studies have analyzed the changes attributed to 2013 updated guidelines, and majority of them found increase in positive and equivocal cases. However, the precise implication of these updated guidelines is still contentious, in spite of the latest update (2018 guidelines) addressing some of the issues. We conducted systematic review and meta- analysis to see the impact of 2013 guidelines on various HER2 reporting categories by both FISH and IHC.

Materials and Methods:

After extensively searching the pertinent literature, 16 studies were included for the systematic review. We divided our approach in three strategies: (1) Studies in which breast cancer cases were scored for HER2 by FISH or IHC as a primary test concurrently by both 2007 and 2013 guidelines, (2) Studies in which HER2 results were equivocal by IHC and were followed by reflex-FISH test by both 2007 and 2013 guidelines, and (3) Studies in which trends of HER2 reporting were compared in the two periods before and after implementation of updated 2013 guidelines. All the paired data in these respective categories was pooled and analyzed statistically to see the overall impact of the updated guidelines.

Results:

In the first category, by pooled analysis of primary FISH testing there has been a significant increase in the equivocal cases (P< 0.001) and positive cases (P= 0.037). We also found 8.3% and 0.8% of all the negative cases from 2007 guidelines shifted to equivocal and positive categories, respectively. Similarly by primary IHC testing there has been a significant increase in both equivocal cases (P< 0.001) and positive cases (P= 0.02). In the second category of reflex-FISH testing there was a substantial increase in the equivocal cases (P< 0.0001); however there is insignificant decrease (10% to 9.7%;P= 0.66) in the amplified cases. In the third approach for evaluating the trend, with the implementation of 2013 guidelines, there was increase in the equivocal category (P= 0.025) and positive category (P= 0.0088) by IHC. By FISH test also there was significant increase in the equivocal category (P< 0.001) while the increase in the positive category was non-significant (P= 0.159).

Conclusions:

The updated 2013 guidelines has significantly increased the positive and equivocal cases using primary FISH or IHC test and with further reflex testing, thereby increasing the double equivocal cases and increasing the cost and delaying the decision for definite management. However, whether the additional patients becoming eligible for HDT will derive treatment benefit needs to be answered by further large clinical trials.

Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline Focused Update

PURPOSE.—

To update key recommendations of the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) human epidermal growth factor receptor 2 (HER2) testing in breast cancer guideline.

METHODS.—

Based on the signals approach, an Expert Panel reviewed published literature and research survey results on the observed frequency of less common in situ hybridization (ISH) patterns to update the recommendations.

RECOMMENDATIONS.—

Two recommendations addressed via correspondence in 2015 are included. First, immunohistochemistry (IHC) 2+ is defined as invasive breast cancer with weak to moderate complete membrane staining observed in >10% of tumor cells. Second, if the initial HER2 test result in a core needle biopsy specimen of a primary breast cancer is negative, a new HER2 test may (not "must") be ordered on the excision specimen based on specific clinical criteria. The HER2 testing algorithm for breast cancer is updated to address the recommended workup for less common clinical scenarios (approximately 5% of cases) observed when using a dual-probe ISH assay. These scenarios are described as ISH group 2 ( HER2/chromosome enumeration probe 17 [CEP17] ratio ≥2.0; average HER2 copy number <4.0 signals per cell), ISH group 3 ( HER2/CEP17 ratio <2.0; average HER2 copy number ≥6.0 signals per cell), and ISH group 4 ( HER2/CEP17 ratio <2.0; average HER2 copy number ≥4.0 and <6.0 signals per cell). The diagnostic approach includes more rigorous interpretation criteria for ISH and requires concomitant IHC review for dual-probe ISH groups 2 to 4 to arrive at the most accurate HER2 status designation (positive or negative) based on combined interpretation of the ISH and IHC assays. The Expert Panel recommends that laboratories using single-probe ISH assays include concomitant IHC review as part of the interpretation of all single-probe ISH assay results.

Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline Focused Update

Purpose To update key recommendations of the American Society of Clinical Oncology/College of American Pathologists human epidermal growth factor receptor 2 (HER2) testing in breast cancer guideline. Methods Based on the signals approach, an Expert Panel reviewed published literature and research survey results on the observed frequency of less common in situ hybridization (ISH) patterns to update the recommendations. Recommendations Two recommendations addressed via correspondence in 2015 are included. First, immunohistochemistry (IHC) 2+ is defined as invasive breast cancer with weak to moderate complete membrane staining observed in > 10% of tumor cells. Second, if the initial HER2 test result in a core needle biopsy specimen of a primary breast cancer is negative, a new HER2 test may (not "must") be ordered on the excision specimen based on specific clinical criteria. The HER2 testing algorithm for breast cancer is updated to address the recommended work-up for less common clinical scenarios (approximately 5% of cases) observed when using a dual-probe ISH assay. These scenarios are described as ISH group 2 ( HER2/chromosome enumeration probe 17 [CEP17] ratio ≥ 2.0; average HER2 copy number < 4.0 signals per cell), ISH group 3 ( HER2/CEP17 ratio < 2.0; average HER2 copy number ≥ 6.0 signals per cell), and ISH group 4 ( HER2/CEP17 ratio < 2.0; average HER2 copy number ≥ 4.0 and < 6.0 signals per cell). The diagnostic approach includes more rigorous interpretation criteria for ISH and requires concomitant IHC review for dual-probe ISH groups 2 to 4 to arrive at the most accurate HER2 status designation (positive or negative) based on combined interpretation of the ISH and IHC assays. The Expert Panel recommends that laboratories using single-probe ISH assays include concomitant IHC review as part of the interpretation of all single-probe ISH assay results. Find additional information at www.asco.org/breast-cancer-guidelines .

Immunohistochemistry and alternative FISH testing in breast cancer with HER2 equivocal amplification

Purpose

While HER2 testing is well established in directing appropriate treatment for breast cancer, a small percentage of cases show equivocal results by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). Alternative probes may be used in equivocal cases. We present a single community-based institution’s experience in further evaluating these cases.

Patients and methods

Between 2014 and 2016, 4255 samples were submitted for HER2 amplification testing by alternative probes, TP53, RAI1, and RARA. Of the patients tested by FISH, 505/3908 (12.9%) also had IHC data.

Results

Most (73.9%) FISH equivocal cases remained equivocal after IHC testing. However, 50.5% of equivocal cases were classified as HER2 amplified by alternative probes. Most cases were positive by more than one probe: 78% of positive cases by RAI1 and 73.9% by TP53. There was a significant difference between IHC and FISH alternative testing (p < 0.0001) among the equivocal cases by conventional FISH testing, 44% of IHC negative cases became positive while 36% of the positive IHC cases became negative by alternative FISH testing. Available data showed that 41% of patients were treated with palbociclib and were positive by alternative FISH.

Conclusion

The prevalence of double HER2 equivocal cases and the discrepancy between IHC and alternative FISH testing suggest that FISH alternative testing using both RAI1 and TP53 probes is necessary for conclusive classification. Because almost half of FISH equivocal cases converted to HER2 amplified upon alternative testing, clinical studies to determine the benefit of anti-HER2 therapy in these patients are urgently needed.