Changes in the Detection of Human Epidermal Growth Factor Receptor 2 Gene (HER-2) Status for HER-2 Fluorescent In Situ Hybridization Testing
Breast cancer (BC) remains a significant global health challenge, with HER-2-positive subtypes accounting for 15%–20% of cases. The overexpression or amplification of the HER-2 gene correlates with aggressive tumor behavior and poorer prognosis, but advances in anti-HER-2 therapies, such as trastuzumab, have transformed clinical outcomes. However, the accurate determination of HER-2 status remains contentious due to evolving diagnostic guidelines and technical variability. This study examines the clinical implications of revised HER-2 fluorescence in situ hybridization (FISH) testing criteria outlined by the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) across different iterations (2007, 2013, and 2018), focusing on prognosis and therapeutic decision-making in equivocal cases.
HER-2 Testing Guidelines and Clinical Implications
The ASCO/CAP guidelines aim to standardize HER-2 testing to identify patients most likely to benefit from anti-HER-2 therapy. The 2013 guidelines redefined HER-2 positivity for FISH as a HER-2-to-CEP17 ratio ≥2.0 or an average HER-2 copy number ≥6.0 signals per tumor cell, with equivocal ranges introduced for cases falling between thresholds. The 2018 update further refined these criteria, reclassifying some equivocal cases as HER-2 negative if the HER-2-to-CEP17 ratio was <2.0 despite elevated HER-2 copy numbers (≥4.0 and <6.0). These changes aimed to reduce false-positive interpretations but raised questions about whether reclassified patients might still benefit from targeted therapies.
Study Design and Patient Stratification
This retrospective analysis included 1,208 patients with histologically confirmed HER-2 immunohistochemistry (IHC) 2+ breast cancer who underwent surgical resection at Peking Union Medical College Hospital between 2007 and 2017. Patients were stratified into five groups based on HER-2 FISH results:
- Group 1: HER-2/CEP17 ratio <2.0, average HER-2 copies <4.0 (n=791)
- Group 2: HER-2/CEP17 ratio <2.0, average HER-2 copies 4.0–6.0 (n=167)
- Group 3: HER-2/CEP17 ratio <2.0, average HER-2 copies ≥6.0 (n=29)
- Group 4: HER-2/CEP17 ratio ≥2.0, average HER-2 copies <4.0 (n=20)
- Group 5: HER-2/CEP17 ratio ≥2.0, average HER-2 copies ≥4.0 (n=201)
Clinical outcomes, including recurrence-free survival (RFS), distant recurrence-free survival (DRFS), disease-free survival (DFS), and overall survival (OS), were analyzed over a median follow-up period. Clinicopathological factors such as age, tumor size, hormone receptor status, and treatment regimens were also evaluated.
Key Findings on Survival Outcomes
The 5-year survival rates across groups revealed distinct prognostic patterns:
- RFS: Group 1–5 showed 96.1%, 95.0%, 96.6%, 88.7%, and 95.0%, respectively, with no statistically significant intergroup differences (p>0.05).
- DRFS: Rates were 91.5%, 86.5%, 82.8%, 85.0%, and 89.9%, respectively. A notable disparity emerged between Group 1 and Group 2 (p=0.011).
- DFS: Rates declined to 89.2%, 82.9%, 82.8%, 73.8%, and 85.4%, with significant differences among groups (p=0.038) and pronounced divergence between Group 1 and Group 2 (p=0.008).
- OS: All groups exhibited high survival rates (96.2%, 93.3%, 89.5%, 100.0%, and 94.6%), with no significant differences.
Group 2, comprising patients reclassified as HER-2 negative under 2018 guidelines (HER-2/CEP17 ratio <2.0 but HER-2 copies 4.0–6.0), demonstrated worse DRFS and DFS compared to Group 1. This group had limited access to trastuzumab, with only 4.2% receiving anti-HER-2 therapy, likely contributing to inferior outcomes. In contrast, Groups 3–5, where trastuzumab usage was higher (up to 60% in some subgroups), showed no significant survival disparities relative to Group 1.
Clinicopathological and Therapeutic Considerations
Patients in Group 4 (HER-2/CEP17 ratio ≥2.0, HER-2 copies <4.0) were younger at diagnosis (p=0.005), but no other demographic or tumor characteristics differed significantly across groups. Distant metastases occurred in 9.8% of the cohort, primarily involving bone (54 cases), followed by multiple sites (37 cases), lung (18 cases), brain (6 cases), and liver (5 cases). Breast-related mortality accounted for 93% of deaths (54/58).
The study highlighted the impact of evolving HER-2 classification on therapeutic eligibility. For instance, Group 2 patients, previously classified as equivocal under 2013 guidelines, were excluded from anti-HER-2 therapy under the 2018 framework. However, their poorer DFS and DRFS outcomes suggest that this reclassification may overlook a subset of patients who could benefit from targeted treatment. These findings align with prior research, such as the BCIRG trials, which reported no significant outcome differences between patients with HER-2/CEP17 ratio <2.0 and HER-2 copies <4.0 versus those with HER-2 copies 4.0–6.0.
Limitations and Future Directions
The retrospective, single-center design and unequal group sizes (e.g., Group 3 and 4 had only 29 and 20 patients, respectively) limit the generalizability of these findings. Additionally, variations in trastuzumab administration across groups, influenced by evolving guidelines and socioeconomic factors, complicate outcome interpretation. Prospective studies with standardized treatment protocols are needed to validate whether patients reclassified as HER-2 negative under updated criteria retain a biological rationale for anti-HER-2 therapy.
Conclusion
This study underscores the clinical consequences of revising HER-2 FISH testing criteria, particularly for patients with HER-2/CEP17 ratio <2.0 and HER-2 copies 4.0–6.0. While recent guidelines aim to reduce diagnostic ambiguity, the inferior survival outcomes in Group 2 suggest that reclassifying these patients as HER-2 negative may inadvertently exclude individuals who could benefit from targeted therapies. Clinicians and pathologists must weigh biological heterogeneity, technical variability, and therapeutic context when interpreting HER-2 status. Further research is critical to optimizing guideline-driven HER-2 testing and ensuring equitable access to life-saving treatments.
doi.org/10.1097/CM9.0000000000001733
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