Differential prognostic value of positive HER2 status determined by immunohistochemistry or fluorescence in situ hybridization in breast cancer.

PURPOSE: Human epidermal growth factor-receptor-2 (HER2) is a membrane-tyrosine-kinase that is amplified/overexpressed up to 20% in breast cancer. HER2 positive status is associated with faster disease progression, higher metastatic potential, and shorter disease-free/overall survival and also has emerged as an important therapeutic target in breast cancer. HER2 status can be determined by in-situ-hybridization (ISH) or immunohistochemistry (IHC). Although the concordance rate between ISH and IHC is well-known, the prognostic power of both technologies if tested in parallel on the same tumor has not been studied extensively. METHODS: In this study we retrospectively analyzed a large HER2 positive breast cancer cohort tested both with fluorescence labeled ISH (FISH) and IHC in parallel on each case. We stratified HER2 positive results by FISH and IHC with long-term overall survival, 5-year survival and metastases/recurrence rates. Positive HER2 status both FISH and IHC was available in 364 patients. RESULTS: The number of HER2 FISH-positive and FISH-negative patients was 342 and 22, respectively. The number of HER2 IHC 0/1 + , IHC 2 + , and IHC 3 + patients was 12, 42, and 310, respectively. Among the patients with IHC 3 + status, 288 were FISH-positive and 22 FISH-negative. HER2 status determined by FISH correlated with clinical outcomes (overall survival and with metastases/recurrence, p = 0.036, p = 0.039), whereas HER2 status determined by IHC did not. CONCLUSION: Our results indicate that prognostic information in HER2 positive breast cancer also depends on the methodology of how positivity was determined. In our cohort, FISH was superior to IHC based positive HER2 status.

HER2/CEP17 Ratios and Clinical Outcome in HER2-Positive Early Breast Cancer Undergoing Trastuzumab-Containing Therapy.

BACKGROUND: Adjuvant therapy comprising the HER2 receptor antagonist trastuzumab is associated with a significant improvement in disease-free and overall survival as compared to chemotherapy alone in localized HER2-positive breast cancer (BC). However, a subset of HER2-positive tumors seems to respond less favorably to trastuzumab. Various mechanisms have been proposed for trastuzumab resistance, such as high HER2 to Chromosome 17 FISH (HER2/CEP17) ratios and the possibility that single agent trastuzumab may not suffice to efficiently block HER2 downstream signaling thresholds. In a retrospective analysis we evaluated whether HER2/CEP17 ratios might have an impact on disease-free survival (DFS). METHODS: Clinical records of Stage I-III BC patients with HER2-positive tumors were reviewed at our institution from 2007-2013. We analyzed demographics, tumor characteristics including tumor size and grade, lymph node involvement and estrogen receptor expression as well as treatment with respect to chemotherapeutic regimens from the clinical charts. HER2/CEP17 ratios were determined by routine pathology analysis using in situ fluorescent hybridization (FISH). Upon statistical preview we defined three groups of HER2 amplification based on FISH ratio (2.2 to 4, >4 to 8, >8), in order to evaluate an association between HER2 gene amplification and DFS with trastuzumab containing therapies. DFS was analyzed using Cox-regression. RESULTS: A total of 332 patients with HER2-positive BC were reviewed. Median age was 54 (range 23-89) years. The majority of tumors were classified T1 (50%) or T2 (39%), node negative (52%) and of high grade G3 histology (70%). We identified 312 (94%) tumors as immunohistochemistry (IHC) score 3+ and HER2/CEP17 ratios were available from 278 patients (84%). 30% (N = 84) had tumors with high HER2/CEP17 ratios (>8). Univariate analysis found no correlation between outcome, age, histological grade, sequence as well as anthracycline content of chemotherapy. However, a prognostic impact was detected for tumor size (p = 0.02), nodal status (p<0.01), proliferation index (p<0.01), level (≥20%) of estrogen receptor expression (p = 0.03) and neoadjuvant therapeutic setting (p = 0.03), respectively. Importantly, univariate and multivariable analysis revealed that standard trastuzumab containing chemotherapy resulted in impaired disease free survival among tumors with FISH ratio >8 (p<0.01). Although less pronounced, a similar association was found also with respect to high HER2 gene copy numbers (>12) and DFS (p = 0.01). CONCLUSIONS: In early BC patients, tumors with high HER2 amplification ratios (>8), may less likely respond to standard trastuzumab-containing therapies. Although, we obtained a similar effect for high HER2 gene copy numbers, this provides only an indirect speculation and not a proof that high HER2/CEP17 ratios may induce HER2 resistance.