Abstract P1-03-02: ASCO/CAP human epidermal growth factor receptor-2 (HER2) in situ hybridization (ISH) categories evaluated by quantitative HER2 protein diagnostic methodologies: A comparative analysis

Background: In 2013, the ASCO/CAP consensus panel published updated guidelines for HER2 testing in breast cancer that modified the definition of HER2 amplification by in situ hybridization (ISH), creating five new prognostic categories (group 1: classic amplified, group 2: monosomy, group 3: co-amplified (polysomy), group 4: equivocal, and group 5: classic non-amplified). Patients determined to be ISH amplified, were considered eligible for HER2-directed therapy. Concern over whether patients from non-classic groups 2-4 would benefit from treatment has led to the recent publication of the 2018 HER2 focused update. This update has modified the criteria for interpreting these ISH categories, recommending that the final diagnosis take into consideration a combination of HER2 immunohistochemistry (IHC) and ISH results. With increased emphasis on the HER2 protein assessment, it has prompted us to quantitatively examine HER2 protein expression in the ISH categories, using two different novel technologies. Materials & Methods: A cohort of 170 cases (URMC) and 102 cases (PSHMC) of invasive breast cancers, which had previously undergone HER2 IHC and ISH testing, were selected for this study. Cases were sorted and categorized into the HER2 ISH categories defined by ASCO/CAP. HER2 protein expression was quantitatively measured in the URMC and PSHMC cohorts using a novel immunodetection methodology (streptavidin-coated Phosphor-Integrated Dot (PID) fluorescent nanoparticles), and a novel dual-antibody, proximity-binding immunoassay (HERmark® Breast Cancer Assay, Monogram Biosciences, South San Francisco, California), respectively. HER2 protein expression was compared to the HER2 FISH and IHC results by ASCO/CAP category. Results: Cases in group 1 had a significantly (p < 0.01) higher average PID/cell and HERmark compared to cases in groups 2-5 (Table 1). Cases in groups 2-4 showed lower quantitative levels of HER2 protein expression, similar to the classic non-amplified cases (group 5). Group 1 was further divided into three subgroups (Table 2): Group A - ISH high-level amplified (ratio > 2, HER2 > 6, CEP17 < 2.7), Group B - amplified with elevated CEP17 (ratio > 2, CEP17 > 2.7), and Group C - low-level amplified (ratio > 2, HER2 > 4 and < 6). Group A and B had a significantly (p < 0.01) higher average PID/cell and HERmark compared to Group C. Group C was more comparable to cases in groups 2-5 (Table 1). Conclusion: Our results suggest that quantitative assessment of HER2 protein expression may help to further classify cases for HER2 status for targeted therapy, supporting the 2018 ASCO/CAP recommendation that non-classic ISH results might be resolved by evaluating protein expression. Follow up studies with a larger patient cohort and dual quantitative assessment are warranted.

Average PID/cell and HERmark in ASCO category groupsASCO category groupN (URMC)PID/cell (URMC)*N (PSHMC)HERmark (PSHMC)*18888.07761.521011.20N/A32016.0213.84238.5315.95296.3208.3*averageTable 2:Average PID/cell and HERmark in subgroups of Group 1SubgroupN (URMC)PID/cell (URMC)*N (PSHMC)HERmark (PSHMC)*A24157.66465.7B34101.61044.1C3016.9329.8*average

Citation Format: Buscaglia B, Turner B, Goda H, Huang W, Leitzel K, Natori T, Nakano Y, Okada H, Sperinde J, Ali S, Vasekar M, D'Aguiar M, McMahon L, Henry J, Lipton A, Hicks D. ASCO/CAP human epidermal growth factor receptor-2 (HER2) in situ hybridization (ISH) categories evaluated by quantitative HER2 protein diagnostic methodologies: A comparative analysis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-03-02.

Abstract P2-05-21: Predictive value of quantitative HER2 and HER3 levels combined with downstream signaling markers in HER2-positive advanced breast cancer patients treated with lapatinib

Background: Clinical correlates of lapatinib resistance have not been well defined. Previous studies implicated genes regulated by the estrogen receptor (ER) and activation or mutation of proteins downstream from HER family receptors. In the current study, HER2 and HER3 expression levels were quantitatively measured using a VeraTag® fluorescence-based assay, in addition to seven downstream signaling proteins determined by IHC. All biomarkers were correlated with overall survival (OS) in patients treated with lapatinib.

Methods: Formalin-fixed, paraffin-embedded samples were obtained from the primary tumor of 191 patients treated with lapatinib plus capecitabine following progression on trastuzumab. The HERmark® Breast Cancer Assay (Monogram Biosciences, South San Francisco) was used to quantify HER2 protein expression levels. HER3 protein expression was quantified using the VeraTag® technology (Monogram Biosciences). Expression of ER, PTEN, Cyclin E, HIF-2alpha, p-p70S6K, p-AMPK and p-MAPK were determined by IHC (Duchnowska et al., Oncotarget 2016; 7:550). OS analyses of HER2 and HER3 were stratified by key clinical variables, including stage and presence of a brain metastasis prior to lapatinib-based therapy.

Results: Among the downstream signaling molecules, HIF-2alpha (r = -0.23; p = 0.047) and ER (r = -0.27; p = 0.005) were negatively correlated with HER2 expression after adjustment for multiple testing. PTEN appeared to correlate with HER3, but was not significant after adjustment for multiple testing. OS was significantly shorter for both those below the cut-off level of positivity by the HERmark assay (HR = 1.8; p = 0.029), and those with above median HER2 levels (HR = 1.7; p = 0.009), as compared to cases with in between levels. The relationship between HER2 and OS is also captured by a U-shaped, parabolic function in HER2 (p = 0.005). Elevated HER3 showed a trend toward a correlation with longer OS (HR = 0.66/log; p = 0.16), somewhat stronger in the ER-negative subset (HR = 0.55/log; p = 0.085) and in the subset with above-median HER2 (0.48/log; p = 0.10), where inhibiting HER2 activation of HER3 may be more important. In multivariate Cox models, HER2 (parabola, intermediate HER2 best, p = 0.001), presence of brain metastases (HR = 2; p < 0.001), ER (HR = 0.60; p = 0.009) and either p-p70S6K (HR = 0.66; p = 0.018) or p-AMPK (HR = 0.67; p = 0.022) were significantly associated with OS (p-p70S6K and p-AMPK were mutually correlated).

Conclusions: Patients with moderately increased HER2 levels may have best outcomes while receiving lapatinib following progression on trastuzumab. This supports recent findings of a less benefit from lapatinib in patients with high HER2 expression (Nunciforo et al., SABCS 2015, P3-07-08). HER3 levels do not seem to substantially impact the prognosis. Further studies are warranted to explore the predictive utility of quantitative HER2 and HER3 in guiding HER2-directed therapies.

Citation Format: Duchnowska R, Sperinde J, Czartoryska-Arlukowicz B, Mysliwiec P, Winslow J, Radecka B, Petropoulos C, Demlova R, Orlikowska M, Kowalczyk A, Lang I, Ziólkowska B, Debska-Szmich S, Merdalska M, Grela-Wojewoda A, Zawrocki A, Biernat W, Huang W, Jassem J. Predictive value of quantitative HER2 and HER3 levels combined with downstream signaling markers in HER2-positive advanced breast cancer patients treated with lapatinib [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-05-21.

Abstract P3-07-09: Quantitative p95HER2 protein expression is predictive of trastuzumab response in HER2-positive metastatic breast cancer

Background: Expression of p95HER2 (p95), a truncated form of the HER2 receptor that lacks the trastuzumab binding site but retains kinase activity, has been reported as a prognostic biomarker for poor outcome in trastuzumab-treated HER2-positive metastatic breast cancer (MBC). However, the ability of p95 to predict trastuzumab benefit has not been demonstrated due to the difficulty in obtaining the appropriate control group, namely HER2+ MBC patients not treated with trastuzumab. In the current study, the predictive value of p95 expression was tested in a cohort comprised of HER2-positive MBC patients treated before the availability of trastuzumab and trastuzumab-treated HER2-positive MBC patients.

Methods: The current cohort was derived from 206 HER2-positive MBC patients in the Munich Cancer Registry with a median follow up of 64 months. Cases were divided between those that received trastuzumab (n=115) and those that were treated before the availability of trastuzumab (n=91). Quantitative p95 protein expression was measured in formalin-fixed paraffin-embedded samples using the p95 VeraTag® assay (Monogram Biosciences), which is specific for the active M611 form of p95. Quantitative total HER2 protein expression was measured using the HERmark® assay (Monogram Biosciences). p95 and HERmark cutoffs were pre-specified (Duchnowska, Clin Cancer Res, 20:2805, 2014 and Huang, Am J Clin Pathol, 134:303, 2010). Analyses with p95 were restricted to samples with confirmed HER2 overexpression by HERmark. All hazard ratios (HR) were stratified by estrogen receptor status and grade.

Results: Consistent with previous training (Sperinde, Clin Cancer Res, 16:4226, 2010) and validation (Duchnowska, Clin Cancer Res, 20:2805, 2014) datasets, subjects treated with trastuzumab experienced a shorter time to progression (TTP) when p95 expression levels were above the cutoff versus below the cutoff (HR = 3.8, p = 0.019). However, only a trend was observed between p95 expression levels and overall survival (HR = 2.2, p = 0.20), possibly due to a lower frequency of events and relatively small sample size. The predictive value of p95 was assessed by determining the benefit of adding trastuzumab to chemotherapy treatment in subsets below and above the p95 cutoff. As expected, patients with p95 below the cutoff experienced significant benefit in TTP from adding trastuzumab (HR = 0.13, p<0.001), whereas patients with p95 above the cutoff experienced less benefit (HR = 0.70, p=0.47). p95 expression level was predictive of trastuzumab response with an interaction p-value of 0.015. The results for OS were similar, however trastuzumab benefit was less distinct between the two groups (interaction p = 0.18); HR = 0.23, p = 0.0013 below the p95 cutoff versus HR = 0.50, p = 0.14 above the p95 cutoff.

Conclusions: In this dataset, quantitative p95 expression was predictive of trastuzumab treatment benefit in MBC. Patients with high p95 expression may be particularly good candidates for dual HER2 blockade, as reported in the NeoALTTO trial (Scaltriti, Clin Cancer Res, 21:569, 2015), or other additional therapies.

Citation Format: Sperinde J, Bachmeier B, Weidler JM, Lie Y, Chenna A, Winslow J, Engel J, Schubert-Fritschle G, Sommerhoff C, Petropoulos C, Bates M, Huang W, Nerlich A. Quantitative p95HER2 protein expression is predictive of trastuzumab response in HER2-positive metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-09.

Abstract P1-08-42: High HER2 expression correlates with response to trastuzumab and the combination of trastuzumab and lapatinib in the NeoALTTO phase III trial

Background: Expression of p95HER2, a truncated form of HER2 lacking the extracellular domain, has been associated with resistance to trastuzumab (T)-based therapy in metastatic breast cancer patients. Conversely, high levels of HER2 have been correlated with increased clinical benefit from anti-HER2 therapy in the neoadjuvant setting. In this work we correlated the expression of p95HER2 and HER2 with pathological complete response (pCR) following T, lapatinib (L) or the combination of both agents (T+L) with paclitaxel.

Methods: p95HER2 and HER2 were quantified by VeraTag® and HERmark® (Monogram Biosciences), respectively, in primary tumors of 455 patients enrolled in the phase III neoadjuvant study NeoALTTO (Baselga J. et al. Lancet, 2012). The relationship of pCR status to p95HER2 and HER2 was studied using logistic regression models, which accounted for stratification factors and treatment. Unless specified, p95HER2 and HER2 were included as log terms.

Results: p95HER2 was measurable in 283 cases (62%) and HER2 in 327 cases (72%). A positive correlation between p95HER2 and HER2 levels was found in the 274 cases (60%) where quantification of both markers was available. Increased HER2 was strongly associated with increased pCR rate in patients treated with the combination of T+L (OR 5.09, 95%CI 2.27-11.44; p<0.01), with a trend observed also in the L-only arm (OR 1.88, 95% CI 0.96-3.70; p = 0.067). Overall, patients with tumors that were HER2-positive (>17.8 RF/mm2) by HERmark had a higher pCR rate than those that were HER2-negative by HERmark (39% vs. 11%, respectively; p<0.001). Increasing p95HER2 levels did not predict for pCR in the L or T+L arms and showed weak evidence (p = 0.073) of an increase in pCR in the T arm.

In an unplanned analysis, we examined the odds of achieving response to anti-HER2 therapy in patients with HER2 levels above and below the median (100 RF/mm2, HER2 entered as a binary covariate). HER2 levels above the median predicted a higher response rate to T (OR 3.6, 95% CI 1.2-11; p<0.05) and, more significantly, to T+L (OR 6.01, 95% CI 2.51-14.4; p<0.001). In particular, patients treated with T+L had a higher probability to achieve pCR compared to T alone when HER2 was above the median (T+L = 73% pCR vs. T = 43% pCR, p<0.01; OR 3.74, 95% CI 1.57-8.90), but not when HER2 was below the median (T+L = 29% pCR vs. T = 19% pCR, p>0.2; OR 1.84, 95% CI 0.74-4.55). When tumors were divided in hormone receptor (HR)-positive and HR-negative groups, total levels of HER2 still predicted response to T or T+L.

Conclusions: Increasing HER2 protein expression correlated with increased benefit of adding L to T compared to T alone. In tumors above the median of HER2 expression, the levels of HER2 predicted for response to both T and T+L. Our interpretation is that, in the neoadjuvant setting, the association between p95HER2 expression and response to anti-HER2 therapy is likely a consequence of the correlation between p95HER2 and total HER2 levels. HER2 expression seems to be a stronger predictor of pCR than p95HER2 for response to T, L and especially, T+L. Future studies to understand the impact of p95HER2 and HER2 expression on disease-free and overall survival following anti-HER2 therapy are warranted.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-42.

Abstract P6-11-07: Quantitative p95HER2 levels in primary breast cancers and in matched brain metastases

Background: Patients with HER2-positive breast cancer are at high risk for brain metastases. A large number of HER2-positive tumors also express p95HER2 (p95), a truncated form of HER2 that lacks the trastuzumab binding site but retains kinase activity. Although p95 expression in primary breast tumors is well studied, the prevalence and significance of p95 expression in brain metastases is unknown. In the current study we examined expression of p95 in brain metastases and in matched primary breast tumors.

Methods: Seventy-five pairs of formalin-fixed paraffin-embedded samples from matched primary breast cancers and brain metastases were assayed for quantitative p95 protein expression using the p95 VeraTag® assay (Clin Cancer Res, 16:4226, 2010) specific for the M611 form of p95. Sufficient material to obtain p95 data in both primary and matched brain metastasis samples was available in 52 cases. In the remaining 23 cases, a p95 measurement was obtained in either the primary or brain metastasis sample. Estrogen (ER) and progesterone (PR) receptor status were scored using immunohistochemistry. Hormone receptor positivity was defined as either ER or PR positive. Quantitative HER2 protein expression was measured using the HERmark® assay. Both the p95 VeraTag assay and the HERmark assay measure tumor-averaged protein expression in units of relative fluorescence per mm2 tumor (RF/mm2). Measurements of p95 > 2.8 RF/mm2 and HER2 > 17.8 RF/mm2 were considered as positive results.

Results: There was a net increase in p95 expression in brain metastases relative to the matched primary tumor with a median increase of 1.5-fold (p = 0.001, range 0.2-fold to 35-fold). The increase in p95 expression was only weakly correlated with the increase in quantitative HER2 expression (R2 = 0.18; p = 0.0018). Cases with HERmark-positive tumors were more likely to have the largest (≥ 5-fold) increase in p95 expression compared to those with lower HER2 expression (odds ratio = 6.3; p = 0.018). Changes in p95 levels from primary to brain metastasis were unrelated to hormone receptor status (p = 0.59). P95 positivity in the primary tumor correlated with time from breast cancer diagnosis to first progression (HR = 2.2; p = 0.012) when stratified by hormone receptor status and tumor grade. Although there was a trend towards correlation of p95 positivity in the brain metastasis with time from diagnosis to brain metastasis (HR = 1.7; p = 0.058, stratified as above), p95 positivity did not correlate with overall survival from the time of brain metastasis diagnosis (HR = 1.3; p = 0.42, stratified as above).

Conclusions: This is the first study of quantitative p95 expression in matched primary tumors and brain metastases. Brain metastases of breast cancer show significant increases in p95 protein expression compared to matched primary tumors. These data provide a rationale for future correlative studies on p95 levels in brain metastases.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-11-07.

Abstract P1-08-23: Potential biomarkers of long-term benefit from single-agent trastuzumab or lapatinib in HER2-positive metastatic breast cancer

Purpose: In 2009 we started a prospective, randomized Phase II trial to evaluate HER2-targeting without chemotherapy (CT) in HER2-positive (HER2+) metastatic breast cancer (MBC) patients (pts). Although the study was prematurely closed because of slow accrual, we decided to analyze the primary tumors in order to identify possible biomarkers that could identify, among the enrolled pts, those deriving the longest lasting benefit from HER2-targeting without CT.

Experimental Design: In the HERLAP study (NCT00842998), pts with HER2+ MBC were randomized to trastuzumab or lapatinib as first-line therapy. Patients showing radiological signs of tumor regression after 8 weeks of treatment were allowed to continue on single agent anti-HER2 therapy until disease progression. CT was added to anti-HER-2 therapy in pts failing to achieve tumor regression at the 8-week evaluation and in those progressing at any time. Expression analysis of 105 selected genes was performed from formalin-fixed paraffin-embedded primary tumor samples. The research-based PAM50 intrinsic subtypes (Luminal A, Luminal B, HER2-enriched and Basal-like) and the normal breast-like group were also identified. Additionally, quantitative HER2 (H2T) and p95HER2 (p95) protein expression were evaluated using the HERmark® assay and the p95 VeraTag® assay, respectively. Potential predictors of persistence on protocol (PP, time from randomization to addition of chemotherapy to anti HER2-therapy or death from any cause) were studied by univariate and multivariate analysis.

Results: Nineteen patients were enrolled. Median overall survival was 43 months and median PP was 3.8 months (0.8-38.8+) with 4 pts (21.1%) persisting on single agent T or L for longer than 12 months (14.9-38.8+ months). Seventeen pts were evaluable for PP. Gene expression analysis revealed that high expression of the 17q12-21 amplicon genes HER2 and GRB7, and the PAM50 HER2-enriched intrinsic profile, were significantly associated with longer PP. Conversely, high expression of luminal-related genes such as PGR, MDM2 and PIK3CA, or the PAM50 luminal intrinsic profile, were found associated with reduced PP. Quantitative H2T and p95 expression revealed that, increasing H2T/p95 ratio significantly associated with longer PP (HR 0.969, p = 0.010).

When analyzed as a multivariable model, PAM50 intrinsic subtype and H2T/p95 ratio dichotomized around the median value independently predicted for longer PP (PAM50 non-luminal vs. Luminal A+B, HR 0.164, p = 0.078 and H2T/p95 ratio higher vs. lower/equal, HR 0.294, p = 0.062 respectively).

Conclusions: Our data suggest that tumors belonging to the PAM50 “HER2-enriched” subtype tumors and/or with high H2T/p95 protein expression ratio are exquisitely sensitive to anti HER2-agents. MBC pts with these tumors may be candidates for studies aimed at establishing chemotherapy-free approaches.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-08-23.

A phase II study of ixabepilone and trastuzumab for metastatic HER2-positive breast cancer

BACKGROUND

A multicenter NCI-sponsored phase II study was conducted to analyze the safety and efficacy of the combination of ixabepilone with trastuzumab in patients with metastatic HER2-positive breast cancer.

PATIENTS AND METHODS

Two cohorts were enrolled: cohort 1 had received no prior chemotherapy or trastuzumab for metastatic disease and cohort 2 had received 1-2 prior trastuzumab-containing regimens for metastatic disease. Patients in both cohorts received ixabepilone 40 mg/m(2) as a 3-h infusion and trastuzumab on day 1 of a 21-day cycle. Tumor biomarkers that may predict response to trastuzumab were explored.

RESULTS

Thirty-nine women entered the study with 15 patients in cohort 1 and 24 patients in cohort 2. Across both cohorts, the overall RR was 44%, with a clinical benefit rate (CR + PR + SD for at least 24 weeks) of 56%. Treatment-related toxic effects included neuropathy (grade ≥2, 56%), leukopenia (grade ≥2, 26%), myalgias (grade ≥2, 21%), neutropenia (grade ≥2, 23%), and anemia (grade ≥2, 18%).

CONCLUSIONS

This represents the first study of the combination of ixabepilone with trastuzumab for the treatment of metastatic HER2-positive breast cancer. These results suggest that the combination has encouraging activity as first and subsequent line therapy for metastatic breast cancer.

Abstract P2-10-31: Correlation of quantitative p95HER2 and total HER2 levels with clinical outcomes in a combined analysis of two cohorts of trastuzumab-treated metastatic breast cancer patients

Background: Expression of p95HER2 (p95), a truncated form of HER2 also known as p110 or M611-CTF, is a possible trastuzumab resistance mechanism and has been associated with poor prognosis in trastuzumab-treated HER2-positive metastatic breast cancer (MBC). Previously we reported on optimal clinical cutoffs for quantitative p95 (Clin Cancer Res, 16:4226, 2010) and quantitative HER2 protein expression (H2T) by HERmark® (Cancer, 116:5168, 2010) that defined patient subsets with different progression-free survival (PFS). These cutoffs were confirmed in an independent trastuzumab-treated MBC cohort (ASCO 2011, #586). Here, using individual patient data, we performed an analysis on the combined data set of 243 cases from the discovery and validation cohorts to derive optimal cutoffs for quantitative p95 and H2T.

Methods: Both quantitative H2T (HERmark, Monogram Biosciences) and p95 assays employed the VeraTag® method to quantify protein expression in formalin-fixed, paraffin-embedded tumor samples from two cohorts of 101 and 142 cases of trastuzumab-treated MBC with 7.4 and 9.2 months median PFS, respectively. All analyses were stratified by hormone receptor status, tumor grade (3 vs. 1+2) and cohort. H2T measurements were compared to pre-specified cutoffs for HERmark negative (H2T<10.5 Relative Fluorescence/mm2 tumor [RF/mm2]) and HERmark positive (H2T>17.8 RF/mm2), derived from the <5th percentile of centrally determined HER2-positives and the >95th percentile of centrally determined HER2-negatives, respectively, within a reference database of 1,090 breast cancer patient samples.

Results: Patients classified as HERmark-positive had longer PFS than those classified as HERmark-negative (HR = 0.52; p = 0.0006; medians 10.0 and 5.9 months). The previously determined optimal H2T cutoff of 13.8 RF/mm2 in the center of the HERmark-equivocal zone, gave a similar result (HR = 0.54; p = 0.0005). This was close to the optimal cutoff of 12.75 RF/mm2 (HR = 0.48; p < 0.0001, unadjusted) for the combined data set. The PFS for the small group of patients in the HERmark-equivocal zone (n = 20) was more similar to the HERmark-negatives (equivocal vs. negative: HR=0.98; p = 0.9) than the HERmark-positives (positive vs. equivocal: HR=0.57; p = 0.057). The pre-specified p95 cutoff at 2.8 RF/mm2 separated the 174 HERmark-positive cases into two groups of longer (p95<2.8 RF/mm2) vs. shorter PFS (HR = 1.9; p = 0.0014; medians 13.1 and 7.4 months). Increasing continuous p95 also correlated with shorter PFS (HR = 1.9/log; p = 0.022) in the HERmark-positive subset. An optimal p95 cutoff was identified at 2.7 RF/mm2 (HR = 2.0; p = 0.0009, unadjusted), although a slightly higher local HR maximum was found at 1.55 RF/mm2 (HR = 2.3; p = 0.0004, unadjusted).

Conclusions: HERmark positive and negative categories, defined by analytical comparison with centrally determined HER2 status, were confirmed to have significantly different PFS in trastuzumab-treated MBC patients. The optimal H2T clinical cutoff for this combined analysis was centered in the HERmark analytical equivocal zone. An optimal p95 clinical cutoff of 2.7 RF/mm2 derived from this combined analysis was nearly identical to the previously established cutoff of 2.8 RF/mm2.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-10-31.

Abstract P2-10-16: Quantitative HER3 protein expression and PIK3CA mutation status in matched samples from primary and metastatic breast cancer tissues and correlation with time to recurrence

Background: HER3 is thought to play a prominent role in resistance to HER2-directed breast cancer therapies. Recent data suggest that HER3 levels also influence HER2-normal breast tumor biology. HER3 and PI3K signaling are linked in that in HER3 signaling activates PI3K and inhibition of PI3K activity can upregulate HER3 expression. Here, we measured quantitative HER3 protein expression levels and PIK3CA mutation status in matched tissues from the primary tumor and site of metastasis to assess correlations with time to recurrence.

Methods: 44 pairs (8 HER2+ by HERmark®) of matched tissues from the primary tumor and the site of metastasis were evaluated for HER3 protein expression using a sensitive, quantitative assay for HER3 protein expression in FFPE tissue sections (VeraTag®). Matched samples were also evaluated for quantitative HER2 expression (HERmark) and for PIK3CA mutations at exon 9 (E542K and E545K) and exon 20 (H1047R).

Results: HER3 protein expression at the metastatic site was largely independent of HER3 levels at the primary site (Spearman p = 0.50) in contrast to HER2 expression (Spearman p = 0.0004). HER3 expression in the primary tumor correlated with time to recurrence (TTR) (HR = 2.0 per 2-fold increase in HER3; p < 0.0001). Conversely, HER3 expression measured at the site of metastasis was not correlated with TTR (p = 0.55). Estrogen receptor negative tumors were less likely to have PIK3CA mutations (p = 0.023). In cases of primary tumors with PIK3CA mutations, no reversions to wild-type PIK3CA were observed in the metastatic sites. In metastatic tumors, mutations detected in the primary tumor as well as new mutations were observed. A gain of an exon 9 mutation at the metastatic site correlated with shorter TTR (HR = 2.5; p = 0.043). Excluding the 8 samples that were HER2+ by HERmark, longer TTR was observed for patients with PIK3CA mutations in the primary tumor (HR = 0.47; p = 0.042), which is consistent with previous reports. Interestingly, the longer TTR for those with PIK3CA mutations appeared to be dependent on quantitative HER3 protein level (interaction p = 0.065).

Conclusions: HER3 protein expression in matched primary and metastatic breast cancer tissues were unrelated. This may indicate that HER3 protein is influenced by the different tumor microenvironments of the primary and metastatic sites. PIK3CA mutations were either maintained or acquired at metastatic sites. Both low HER3 protein expression and the presence of PIK3CA mutations in the primary tumor but not the metastatic tumor were associated with longer TTR. These observations suggest that HER3 protein expression may be an important prognostic factor for breast cancer progression.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-10-16.

P2-12-05: Correlation between Quantitative HER2 Protein Expression and Risk of Brain Metastases in HER2−Positive Advanced Breast Cancer Patients Receiving Trastuzumab-Containing Therapy

Background. Patients with HER2−positive breast cancer are at particularly high risk for brain metastases; however, the biological basis is not fully understood. Within HER2−positive breast cancer tumors, it is possible to resolve a ∼1.5-log range of HER2 protein expression using a novel quantitative HER2 assay (HERmark®). We investigated the correlation between quantitative HER2 protein expression in primary breast cancers and the time to brain metastases (TTBM) in HER2−positive advanced breast cancer patients treated with trastuzumab.

Methods. The study group included 142 consecutive patients who were administered trastuzumab-based therapy for HER2−positive metastatic breast cancer, defined as 3+ categorical staining by immunohistochemistry (IHC). HER-2/neu gene copy number was subsequently quantified as HER2/CEP17 ratio by central laboratory fluorescence in situ hybridization (FISH). HER2 protein was quantified as total HER2 protein expression (H2T) by the HERmark assay in formalin-fixed, paraffin-embedded primary tumor samples. HER2 variables were correlated with clinical features and TTBM measured from the initiation of trastuzumab-containing therapy.

Results. H2T level (continuous variable) was correlated with shorter TTBM (HR=2.3; p=0.013), whereas HER2 gene amplification by FISH (p=0.28) and continuous HER2/CEP17 ratio (p=0.25) had no significant prognostic impact. The correlation between continuous H2T level and TTBM was confirmed in a multivariate analysis (HR=3.2; p=0.021). Controlling for the competing risk of death from causes other than brain metastases, continuous H2T remained a strong correlate of TTBM (HR=2.7; p=0.0009). In the subset of patients that was centrally-determined HER2 positive by FISH (117 patients), above-median H2T level was significantly associated with shorter TTBM (HR=2.4; p=0.005), whereas this was not true for median FISH/CEP17 ratio (p=0.4). In a multivariate analysis of this subset, continuous H2T (p=0.021) and a time dependent covariate capturing time to non-brain metastases (p=0.0044) were prognostic for TTBM, whereas FISH/CEP17, ER, PgR and grade were not.

Conclusions. These data reveal a strong relationship between quantitative HER2 protein expression levels and the risk of brain relapse in HER2−positive advanced breast cancer patients. Consequently, quantitative assessment of HER2 protein expression may inform and facilitate refinements in therapeutic treatment strategies for selected subpopulations of patients in this group.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-12-05.

Identification of a subpopulation of metastatic breast cancer patients with very high HER2 expression levels and possible resistance to trastuzumab

BACKGROUND

Patients with metastatic breast cancer (MBC) overexpressing HER2 (human epidermal growth factor receptor 2) are currently selected for treatment with trastuzumab, but not all patients respond.

PATIENTS AND METHODS

Using a novel assay, HER2 protein expression (H2T) was measured in formalin-fixed, paraffin-embedded primary breast tumors from 98 women treated with trastuzumab-based therapy for MBC. Using subpopulation treatment effect pattern plots, the population was divided into H2T low (H2T < 13.8), H2T high (H2T ≥ 68.5), and H2T intermediate (13.8 ≤ H2T < 68.5) subgroups. Kaplan-Meier (KM) analyses were carried out comparing the groups for time to progression (TTP) and overall survival (OS). Cox multivariate analyses were carried out to identify correlates of clinical outcome. Bootstrapping analyses were carried out to test the robustness of the results.

RESULTS

TTP improved with increasing H2T until, at the highest levels of H2T, an abrupt decrease in the TTP was observed. KM analyses demonstrated that patients with H2T low tumors [median TTP 4.2 months, hazard ratio (HR) = 3.7, P < 0.0001] or H2T high tumors (median TTP 4.6 months, HR = 2.7, P = 0.008) had significantly shorter TTP than patients whose tumors were H2T intermediate (median TTP 12 months). OS analyses yielded similar results.

CONCLUSIONS

MBC patients with very high levels of H2T may represent a subgroup with de novo resistance to trastuzumab. These results are preliminary and require confirmation in larger controlled clinical cohorts.

Multiple Subtypes of HER-2/Neu-Positive Metastatic Breast Cancer

Background: Using IHC or FISH to select patients for trastuzumab-based therapy, only half of HER2-positive patients show evidence of response. In vitro data implicate HER2:HER3 heterodimers and p95HER2 (p95), the truncated 95-kilodalton C-terminal fragment of HER-2 lacking the trastuzumab binding site, as mediators of resistance to trastuzumab at the receptor level. We have previously reported that central FISH-positive patients with low HER2 protein expression by VeraTag had significantly reduced response to trastuzumab compared to patients who had FISH-positive tumors with high HER2 protein expression (Lipton, SABCS 2008). Adding quantitative measurements of HER3 and p95, we offer evidence for the existence of multiple sub-types of HER2-positive tumors that respond differently to trastuzumab.Methods: Using the VeraTag assay, quantitative protein measurements of HER2, HER3, and p95 were made in FFPE specimens from a cohort of patients with metastatic breast cancer (MBC) and correlated with time to progression (TTP) and overall survival (OS) following treatment with first-line trastuzumab using Kaplan-Meier (KM) and Cox proportional hazards regression analyses.Results: Measurements of HER2 (H2T), HER3 (H3T) and p95 were made in FFPE tumor samples from 95 patients treated with first-line trastuzumab for metastatic breast cancer. Within the group that overexpressed HER2 by the VeraTag Assay (n=60), a group with highly overexpressed HER2 (n=15) had shorter TTP and OS than those that had moderate HER2 overexpression (median TTP 4.6 vs. 12 mos, HR=2.1; p=0.011; median OS 29 vs. 40 mos, HR=2.0; p=0.047). Within the subgroup with moderate H2T overexpression (n=45), bivariate Cox analyses demonstrated that p95 and H3T were independent predictors of TTP (p95 HR=2.1; p=0.031; H3T HR=3.5; p=0.0037). For OS, p95 was significant and H3T showed a strong trend (p95 HR=2.5; p=0.025, H3T HR=2.2; p=0.089). Univariate KM analysis with the p95+ and H3T+ groups combined, gives the results in the table below. These data suggest that HER2-positive breast cancer patients can be classified into at least 4 sub-groups with different outcomes following trastuzumab treatment.Conclusions: These data suggest the existence of multiple subgroups of HER2-positive patients expressing varying HER2, p95, and HER3 levels that experience different clinical outcomes following treatment with trastuzumab. Furthermore, the association of HER3 and p95 overexpression with poor response to trastuzumab in otherwise HER2-positive tumors suggests possible treatment approaches with combinations of targeted therapies.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2030.

Breast Cancer Patients with Very High Tumor HER2 Expression Levels Might Not Benefit from Treatment with Trastzumab Plus Chemotherapy: A Retrospective Exploratory Analysis of the FinHer Trial

Background: FinHer (NEJM 2006) is one of the several prospective randomized clinical trials that show a clinical benefit from trastuzumab added to adjuvant chemotherapy. We have previously reported that patients with metastatic breast cancer who had very high levels of HER2 protein expression as measured by the HERmark assay and who were treated with trastuzumab had similar time-to-progression (TTP) compared to a group of patients who had FISH-negative and HER2 normal cancer suggesting reduced efficacy of trastuzumab when tumor HER2 content is very high (Sperinde, ASCO 2009). Here we investigate the relationship between clinical benefit from trastuzumab and quantitative HER2 protein expression (H2T) as determined by the HERmark assay.Methods: H2T was quantitated by the HERmark assay in 899 formalin-fixed paraffin-embedded specimens from patients enrolled in the FinHer trial; 196 of the samples were HER2-positive by chromogenic in situ hybridization (CISH). Focusing on the HER2-positive patients who were randomized to trastuzumab treatment or control, Cox proportional hazards analyses, sub-population treatment effect pattern plots (STEPP analyses), positional scanning analyses, and Kaplan-Meier analyses were used to identify sub-populations of HER2 over-expressing patients who experienced different clinical outcomes on trastuzumab.Results: Using time to distant recurrence (TDR) and overall survival (OS) as endpoints, Cox proportional hazards analyses treating H2T as a continuous variable failed to show a relationship between HER2 expression levels and clinical benefit from trastuzumab (HR=1, p=ns for both). STEPP analyses were performed to look for non-linear relationships between H2T and clinical outcome. At the highest levels of H2T, the hazard ratio comparing trastuzumab treatment to control approached and exceeded 1. Positional scanning analyses were conducted to identify the optimal cutoff discriminating the very high H2T group. Patients with very high H2T values (&gt;= 125.9) did not benefit from trastuzumab plus chemotherapy treatment relative to controls (HR=1.23, p=0.75 for TDR, HR=1.05, p=0.95 for OS), while those with H2T values &lt;125.9 did (HR=0.52, p=0.05 for TDR, HR=0.48, p=0.1 for OS). The very high H2T group represented 13% of the HER2-positive population compared with 16% in the prior study from Sperinde et al.Discussion: In this exploratory analysis of a prospectively randomized controlled trial of trastuzumab in the adjuvant setting, the 13% of patients with the highest H2T values showed no evidence of clinical benefit from trastuzumab. Potential explanations include insufficient trastuzumab dose, steric hindrance preventing access of trastuzumab to its epitope target under conditions of HER2 over-crowding, or the existence of trastuzumab-resistant forms of HER2 at the highest levels of over-expression (e.g. p95/HER2, HER2:HER3 heterodimers). Although these results are in agreement with prior observations from the metastatic setting, they need to be confirmed in larger randomized trials of trastuzumab in early breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5083.

Discordant HER2 Total and HER2 Homodimer Levels by HERmark Analysis in Matched Primary and Metastatic Breast Cancer FFPE Specimens

Background: HER-2/neu is over-expressed in approximately 25% of primary invasive breast cancers and selection of patients for consideration of trastuzumab is a critical step in defining the treatment plan. We have previously reported that quantitative measurements of HER2 protein expression (H2T) and HER2 homodimers (H2D) using the HERmark assay identifies sub-populations of “HER2-positive” patients (by IHC and/or FISH) that have different clinical outcomes on trastuzumab (Leitzel, ASCO 2008; Lipton, SABCS 2008). Previous studies report up to a 20 % discordance in HER2 status using conventional IHC or FISH analysis between the primary and metastatic breast tumors. Here we correlate HER2 total and homodimer levels in matched primary and metastatic tissue from the same patient.Methods: 27 patients had matched primary and metastatic FFPE (formalin-fixed, paraffin-embedded) specimens tested in the HERmark assay to quantitate and compare their H2T and H2D expression levels.Results: FFPE tissue was available from 27 primary breast cancers and metachronous metastatic sites. Metastatic lesions included 7 skin, 5 lymph node, 3 bone, 3 pleura, 2 brain, 2 chest wall, and 5 other soft tissue lesions. The median elapsed time between matched primary and metastatic sites was 71 mo. (range 9-137 mo). During the time period between the primary specimen harvest and the metastatic biopsy, 6 patients were treated with chemotherapy alone, 10 received hormonal therapy without trastuzumab, 3 patients received trastuzumab, and 3 received no treatment. Treatment was not known for 5 patients. For the whole population, there was a weak to moderate positive correlation between primary and metastatic cancers with H2T (r2=0.36, p&lt;0.001) and for H2D (r2=0.27, p&lt;0.006). Using the optimized time to progression (TTP) positional scanning cutpoints for H2T and H2D defined in our previous reports, 4/20 patients (20%) converted from low to high, and 1/7 (14%) converted from high to low H2T. Using the H2D cutpoint, 7/15 patients (47%) converted from low to high, and 3/12 (25%) converted from high to low H2D. Overall discordance between primary and metastatic sites was 19% for H2T, and 37% for H2D.Conclusions: HERmark analysis of matching primary and metastatic breast cancers revealed 19% discordance for H2T, and 37% for H2D. The most frequent conversion was from low HER2 in the primary tissue to high HER2 in the metastatic site.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2131.

Quantitative measurement of HER3 total protein (H3T) and association with clinical outcome in HER2-positive metastatic breast cancer patients treated with trastuzumab

1021

Background: The heterodimerization of HER3, with HER2 and the subsequent activation of the AKT pathway, has been implicated in both regulation of tumor cell growth and in resistance to HER2 targeted therapies such as trastuzumab. Currently available methods of measuring H3T in formalin-fixed, paraffin-embedded (FFPE) samples are insufficiently sensitive or specific; thus the impact of quantitative measurement of H3T expression on clinical response to trastuzumab has not been evaluated. Methods: We have developed a highly quantitative, accurate, precise, sensitive, and reproducible H3T assay in FFPE samples based on the VeraTag technology platform. Consequently, the H3T assay displays ∼5-fold greater sensitivity than conventional IHC measurements. Additionally, the rank order and accuracy of the H3T measurements were preserved over a wide dynamic range in well-characterized cell line panels. Intra- and inter-assay reproducibility measurements demonstrated 7–11 %CV and 8–16 % CV, respectively. Results: Quantitative levels of HER2 total protein (H2T) and H3T expression were determined by the VeraTag technology in 81 tumors from patients with trastuzumab-treated metastatic breast cancer. A previously reported H2T cutoff was used to sub-divide the patients into HER2-normal (N = 26, median TTP = 4.1 mos) and HER2-overexpressing (N = 55, median TTP = 11.1 mos, HR = 0.43, p = 0.0002) groups. In the HER2-overexpressing group, high H3T expression, as defined by a positional scanning cutoff analysis, predicted shorter median time to progression (N = 25, median TTP = 6.1 mos) compared with low H3T expression (N = 30, median TTP = 13.1 mos, HR = 2.7, p = 0.0002). Univariate Cox proportional hazards analyses examining the HER2-overexpressing subgroup identified H3T (high vs. low) as the most significant predictor of TTP (HR = 2.98, p = 0.0004). Conclusions: These results demonstrate that the accurate and sensitive measurement of H3T in a cohort of patients with HER-2 positive breast cancer predicts TTP in response to trastuzumab and could indicate a population of patients with worse outcome requiring additional therapeutic intervention.

[Table: see text]

Identification of a subpopulation of metastatic breast cancer patients with very high HER2 expression levels and possible resistance to trastuzumab

1059

Background: Many HER2-positive patients with metastatic breast cancer (MBC) fail to respond to trastuzumab. We previously reported that precise quantitation of HER2 expression (H2T) by the HERmark assay identified a sub-population of IHC 3+, FISH(+) (positive) patients with low H2T levels that responded poorly to trastuzumab (Lipton, San Antonio Breast Cancer Symposium 2008, abs #32). Here we identify a sub-population of FISH(+) patients with very high H2T levels, that experience clinical outcomes that are indistinguishable from those of FISH(-) (negative) patients with low H2T levels. Methods: The HERmark assay was used to measure H2T in formalin-fixed, paraffin-embedded (FFPE) primary breast tumor specimens from 99 women treated with trastuzumab for MBC. Specimens were also tested by central FISH. A sub-population treatment effect pattern plot (STEPP) was generated to examine the progression-free survival (PFS) rate at 12 months after treatment with trastuzumab across the distribution of H2T. Kaplan-Meier (KM) analyses were performed comparing the PFS of FISH(-), H2T low (log10H2T < 1.25) patients with those of FISH(+), H2T high (log10H2T ≥ 1.95) and FISH(+), H2T intermediate (1.25 < log10H2T < 1.95) groups. Cutoffs were identified by lowest p-value in a positional scanning analysis. Results: The PFS rate improved gradually with increasing H2T in STEPP analyses. At the highest levels of H2T, an abrupt decrease in the PFS rate was observed, consistent with a reduction in susceptibility to trastuzumab. KM analyses demonstrated that patients who were FISH(+), H2T intermediate had a significantly longer PFS than patients who were FISH(-), H2T low (median PFS 12.6 vs. 4.5 mos; HR = 0.34; p < 0.0001). Patients that were FISH(+), H2T high experienced a PFS that was no better than patients that were FISH(-), H2T low (median PFS 4.6 vs. 4.5 mos; HR = 0.87; p = 0.68). Conclusions: Precise quantitation of HER2 expression levels allows the identification of multiple sub-populations of HER2(+) patients that have different clinical outcomes on trastuzumab. MBC patients with very high levels of H2T could represent a sub-group with de novo resistance to trastuzumab who may benefit from combined therapy.

[Table: see text]

Quantitative HER2 homodimer levels correlate with time to first recurrence in HER2-positive breast cancer patients who did not receive trastuzumab in the adjuvant setting

Abstract #1074

BACKGROUND: HER2-positive breast cancer patients are currently treated with trastuzumab in the adjuvant setting, but prior to 2005 these patients were not routinely offered trastuzumab, creating an opportunity to examine the relationship between HER2 expression and disease progression. The VeraTag technology is a proximity-based assay system that permits quantitative measurements of total HER2 protein expression (H2T) as well as HER2 homodimers (H2D) in formalin-fixed paraffin-embedded (FFPE) tissues. We measured H2T and H2D in a cohort of patients who were HER2-positive but did not receive trastuzumab in the adjuvant setting, and correlated those measurements with time to first recurrence of disease.&#x2028; METHODS: Patients were selected for study because they were treated with a trastuzumab-containing regimen for HER2+ metastatic breast cancer. HER2-positivity was defined as IHC (Herceptest) 3+ or 2+, FISH+ (Vysis). 96 HER2+ patients who had been treated (but not with trastuzumab) in the adjuvant setting were identified. The VeraTag assay was used to quantitate H2T and H2D. Kaplan-Meier and Cox proportional hazards analyses were employed.&#x2028; RESULTS: The distribution of H2T ranged over approximately 135-fold, and H2D varied over approximately 100-fold. In univariate Cox proportional hazards regression analysis, H2T trended toward significance (HR=1.44, p= 0.088) while both H2D (HR=1.39, p=0.022) and the ratio H2D/H2T (HR=2.01, p=0.03) were significantly correlated with time to first recurrence. Kaplan-Meier analysis of the H2T distribution divided into tertiles showed no significant difference in time to first recurrence among the tertiles (HR=0.7, p=0.16 for low vs. high comparison) and no trend was observed (Log Rank test for trend p=0.2). However, the same analyses performed using H2D (HR=0.59, p=0.03) or H2D/H2T (HR=0.56, p=0.01) demonstrated significantly longer time to first recurrence for the lowest tertile compared with the highest tertile respectively. A trend was observed in both cases (H2D: Log Rank p=0.048; H2D/H2T: Log Rank p=0.026)&#x2028; CONCLUSION: In a population of HER2+ patients who did not receive trastuzumab in the adjuvant setting, and who subsequently developed metastatic disease, higher levels of HER2 homodimers and the ratio of homodimers to HER2 total expression correlated with time to first recurrence while total HER2 expression levels did not. These data suggest that measures of the activated forms of HER2 (dimers) may be better predictors of disease progression than simple quantitation of HER2 alone.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1074.

HER2 expression and HER2:HER2 dimerization identifies subpopulations of metastatic breast cancer patients with different probabilities of long-term survival following trastuzumab treatment and with different requirements for concomitant chemotherapy

10557

Background: Selection of patients for treatment with trastuzumab is currently based on the semi-quantitative measurement of HER2 protein expression (IHC) or gene amplification (FISH). We made quantitative measurements of HER2 expression and homodimerization using a novel assay, eTag, and correlated them with overall survival (OS) and time-to-progression (TTP) following trastuzumab treatment in a cohort of patients with metastatic breast cancer (MBC). We also examined the benefit of concomitant chemotherapy (CT) depending on quantitative HER2 expression. Methods: The Jules Bordet cohort (Brussels, Belgium, N=71) had MBC and prior treatment with at least two CT regimens. Patients received trastuzumab alone or combined with predominantly paclitaxel. Independent medical data review and central confirmation of HER2 overexpression by FISH (N=64) or IHC (N=7) were mandatory. The eTag assay was used to quantitate HER2 protein expression and HER2:HER2 dimers in FFPE specimens. eTag measurements were correlated with OS and TTP using Kaplan-Meier and Cox Proportional Hazards regression analyses. Results: Cox analyses identified three independent correlates of OS and TTP: number of metastatic sites (HROS = 2.4/site, 95%CI 1.5–3.9, p = 0.00019), treatment with trastuzumab only (HROS = 2.8, 95%CI 1.1–7.3, p = 0.036), and HER2 expression level (HROS = 0.24/log10(HER2), 95%CI 0.09–0.7, p = 0.0058). Patients with high HER2 (above median expression) experienced better OS than those with low HER2 (HR 0.24, p = 0.0014). Patients with high HER2 expression did not benefit from added CT (HR = 0.95, 95%CI 0.24–3.8, p = 0.94), while patients with low HER2 expression did (trastuzumab alone HR 4.4, 95% CI 1.3–18, p = 0.018). Similar results were observed for HER2:HER2 dimerization. Conclusions: Within a population of patients selected by FISH or IHC to receive trastuzumab, higher HER2 expression or HER2:HER2 dimerization correlated with better outcomes. Patients with high HER2 expression derived no benefit from concomitant CT, while patients with low HER2 expression benefited significantly from the addition of CT to trastuzumab.

No significant financial relationships to disclose.

Quantitative measurement of HER2 expression and HER2 homo-dimerization in formalin-fixed paraffin-embedded (FFPE) breast cancer tissues using a novel proximity-based assay

21023

Background: The best method to assess HER2 status remains controversial. Here we describe a novel assay that provides reliable quantitation of total HER2 (H2T) and HER2 homodimer (H22D) in FFPE tissues. The assay was cross-validated with conventional HER2 tests - immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). Characteristics of the new assay and its potential application as predictive test were explored. Methods: Electrophoretic Tag (eTag) is a proprietary proximity-based technology that measures gene and protein expression. We have developed a novel application of the technology to quantify H2T and H22D in FFPE tissues. The validity of the assay was evaluated by analyzing its performance in cell lines and FFPE breast cancers. IHC (clone CB-11, Ventana) was performed in 174 breast cancers, scored according to standard IHC criteria and Histoscore (H-score), and HER2 gene amplification was evaluated by FISH (PathVysion, Vysis) in 19 breast cancers. eTag assays were performed on the same specimens and the results were compared with those of IHC and FISH. Results: H2T and H22D were proportional to the known expression levels in cell lines. H2T demonstrated a continuous measurement over a wide dynamic range (>2 logs), in contrast with conventional IHC (0, 1+, 2+, 3+). The correlation between H2T and IHC categories was significant (correlation=0.84, p<0.0001 by the Jonckheere-Terpstra test for trend), but overlap of H2T values in adjacent IHC categories was observed. H-score showed good correlation within the lower range of H2T, but plateaued at higher range of H2T. HER2 gene amplification (HER2/CEP17 ratio and gene copy #) by FISH was generally correlated with IHC categories and H2T values. There was a good correlation between H22D and H2T (r2= 0.7, P < 0.001). Conclusions: eTag reliably measures H2T and H22D in FFPE tissues. The continuous measure of H2T over a wide dynamic range and the novel H22D measure provide data superior to conventional HER2 tests by IHC and FISH, but clinical utility of the eTag assay remains to be investigated. eTag has potential as a predictive test for targeted HER2 therapy in breast cancer.

No significant financial relationships to disclose.

Differential survival following trastuzumab treatment based on quantitative HER2 expression and HER2:HER2 dimerization in a clinic-based cohort of patients with metastatic breast cancer

1025

Background: Women with metastatic breast cancer (MBC) that overexpress HER2 experience improved overall survival (OS) when treated with trastuzumab. Immunohistochemistry (IHC) for HER2 protein expression and fluorescence in situ hybridization (FISH) for HER2 gene amplification are the preferred methods of determining HER2 positivity. However, not all HER2 positive patients respond equally well to trastuzumab. We describe the identification of subgroups of HER2+ patients with distinct clinical outcomes based on their quantitative levels of HER2 expression and HER2:HER2 dimerization. Methods: 75 patients with MBC drawn from six oncology clinics in Japan were assayed for HER2 expression and HER2:HER2 dimerization using FFPE specimens by the eTag assay, a proximity-based assay designed to detect and quantify protein-protein dimers. All patients had MBC, were treated with at least one chemotherapy (CT) regimen prior to receiving trastuzumab, and had FFPE specimens available for testing. 33% had at least 3 metastatic sites. 88% were selected for treatment based on IHC and 12% based on FISH. 16% were treated with trastuzumab alone and 84% with trastuzumab plus CT. Median clinical follow-up was 26 months. Cox proportional hazards and Kaplan-Meier (KM) analyses were performed. Results: The most significant variables associated with OS were the presence of brain metastases and the total number of metastases. In the overall population, correcting for the confounding influence of number of metastases, KM analyses demonstrated that patients with higher HER2 expression survived significantly longer than patients with lower HER2 expression (HR for death = 0.36, p = 0.0036). This relationship was even more significant for HER2:HER2 dimers (HR = 0.29, p = 0.0003). Conclusions: In a clinic-based population of Japanese women with MBC treated with heterogeneous prior and concomitant (with trastuzumab) CT regimens, the quantitative levels of HER2 expression and HER2:HER2 dimerization identified subsets of patients within a population of pre-selected HER2+ patients with different probabilities of long-term survival following trastuzumab treatment.

No significant financial relationships to disclose.