Assessing the New American Society of Clinical Oncology/College of American Pathologists Guidelines for HER2 Testing by Fluorescence In Situ Hybridization: Experience of an Academic Consultation Practice

Abstract

Context .- Evaluation of HER2 gene amplification by fluorescence in situ hybridization (FISH) was changed by recent American Society of Clinical Oncology/College of American Pathologists (ASCO-CAP) guidelines. Objective . -To determine frequencies and assess patterns of HER2 protein expression for each ASCO-CAP guideline FISH category among 7526 breast cancers accrued to our consultation practice. Design .- We retrospectively reevaluated the HER2 FISH status of breast cancers in our consultation practice according to ASCO-CAP FISH guidelines, and documented HER2 protein levels in each category. Results . -According to new guidelines, 17.7% of our consultation breast cancers were "ISH-positive" with HER2:CEP17 FISH ratios ≥2.0 and average HER2 gene copies per cell ≥4.0 (group 1); 0.4% were "ISH-positive" with ratios ≥2.0 and average copies <4.0 (group 2); 0.6% were "ISH-positive" with ratios <2.0 and average copies ≥6.0 (group 3); 4.6% were "ISH-equivocal" with ratios <2.0 and average copies ≥4.0 and <6.0 (group 4); and 76.7% were "ISH-negative" with ratios <2.0 and average copies <4.0 (group 5). However, only groups 1 (HER2 amplified) and 5 (HER2 not amplified) agreed with our previously reported status, and only these groups demonstrated the expected immunohistochemistry status, overexpression and low expression, respectively. Groups 2 and 4 breast cancers lacked overexpression, whereas group 3 was not significantly associated with either increased or decreased HER2 expression. Conclusions .- Although the status of approximately 95% of our cases (groups 1 and 5) is not affected by the new guidelines, those of the other 5% (groups 2-4) conflict with previous HER2 gene amplification status and with HER2 status by immunohistochemistry.

Prognostic significance of equivocal human epidermal growth factor receptor 2 results and clinical utility of alternative chromosome 17 genes in patients with invasive breast cancer: A cohort study

“…In our study, equivocal HER2 results approached 4% of the total cases with HER2/CEP17 ratios < 2. This rate is similar to those reported by others . In comparison with HER2‐negative cases, we have demonstrated that HER2‐equivocal results (ie, HER2 copy number, 4 to < 6) in the absence of trastuzumab‐based therapy have no deleterious effects on patient outcomes.…”

“…This rate is similar to those reported by others. 12,14 In comparison with HER2-negative cases, we have demonstrated that HER2-equivocal results (ie, HER2 copy number, 4 to < 6) in the absence of trastuzumab-based therapy have no deleterious effects on patient outcomes. In addition, we have demonstrated that the revised HER2 status due to the use of alternative Ch17 probes is not reflective of patient outcomes.…”

“…Although the goal of the new ASCO/CAP guidelines is to ensure maximal accuracy of HER2 testing, the numbers of equivocal cases have been noted to increase in a significant number of cases. 12,14 The increase in the number of equivocal cases, compounded by the lack of a uniform approach to resolving such problems, makes treatment recommendations for this group of patients difficult. We, therefore, undertook this study to determine the relation between an equivocal HER2 copy number (4 to < 6) and patients' outcomes.…”

HER2 Heterogeneity in Personalized Therapy of Gastro-Oesophageal Malignancies: An Overview by Different Methodologies

“…In detail, many different methods use a single HER2 probe to establish the number of HER2 gene copies, but the most powerful recommendation is to use a dual-probe technique, which allows the determination of the HER2 signals ratio to copies of chromosome 17 and HER2 gene copy number [29]. According to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2013 guidelines, evaluation of HER2 gene amplification by FISH in GEA is comparable to that applied in breast cancer, in which HER2 amplification has been identified as HER2:CEP17 ratio of ≥2 [30]. Studies about concordance between FISH, CISH and SISH have shown excellent rates of 91%-100%, demonstrating all ISH methodologies as suitable for HER2 amplification testing [30].…”

“…According to the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2013 guidelines, evaluation of HER2 gene amplification by FISH in GEA is comparable to that applied in breast cancer, in which HER2 amplification has been identified as HER2:CEP17 ratio of ≥2 [30]. Studies about concordance between FISH, CISH and SISH have shown excellent rates of 91%-100%, demonstrating all ISH methodologies as suitable for HER2 amplification testing [30]. More recently, bright field ISH techniques (CISH and SISH) have emerged as preferred assays, since they allow the histopathological assessment (i.e., selecting areas with an intestinal component in GEA), also in archived and indefinitely retrieved specimens, similarly to DISH [30].…”