Use of the Xpert Breast Cancer STRAT4 for Biomarker Evaluation in Tissue Processed in a Developing Country

Objectives

Breast cancer immunohistochemistry (IHC) biomarker testing is limited in low-resource settings, and an alternative solution is needed. A point-of-care mRNA STRAT4 breast cancer assay for ESR1, PGR, ERBB2, and MKi67, for use on the GeneXpert platform, has been recently validated on tissues from internationally accredited laboratories, showing excellent concordance with IHC.

Methods

We evaluated STRAT4/IHC ESR1/estrogen receptor (ER), ERBB2/human epidermal growth factor receptor 2 (HER2) concordance rates of 150 breast cancer tissues processed in Rwanda, with undocumented cold ischemic and fixation time.

Results

Assay fail/indeterminate rate was 2.6% for ESR1 and ERBB2. STRAT4 agreement with ER IHC was 92.5% to 93.3% and 97.8% for HER2, for standard (1x) and concentrated (4x) reagent-conserving protocols, respectively. Eleven of 12 discordant ER/ESR1 cases were ESR1- negative/IHC-positive. These had low expression of ER by IHC in mostly very small tumor areas tested (7/12; <25 mm²). In two of three discordant HER2 cases, the STRAT4-ERBB2 result correlated with the subsequent fluorescence in situ hybridization (FISH) result. STRAT4-ERBB2 results in 9 of 10 HER2-IHC equivocal cases were concordant with FISH.

Conclusions

The STRAT4 assay is an alternative for providing quality-controlled breast cancer biomarker data in laboratories unable to provide quality and/or cost-efficient IHC services.

Nature or Nurture: Can Prey-Based Diets Influence Species-Specific Physiological Performance Traits of Epidermal Lipid Content and Cutaneous Water Loss?

Epidermal lipids serve as the primary barrier to cutaneous water loss (CWL) and play a significant role in water conservation and homeostasis. Previous studies have shown the correlation between increased aridity of habitats and the amount of epidermal lipids among species. Generally, increased amounts of epidermal lipids lower skin permeability. Species-specific differences in CWL and prey preferences between two sympatric snake species, the Northern Cottonmouth (Agkistrodon piscivorus) and the Eastern Copperhead (Agkistrodon contortrix), motivated us to question if prey-base can result in these observed species-specific differences in CWL. We experimentally controlled the diets for a captive colony of Northern Cottonmouths (A. piscivorus) by feeding either fish (Notemigonus crysoleucas) or mice (Mus musculus) to investigate if diet can affect the quantity and quality of epidermal lipids and the rates of CWL. Snakes fed mice gained consistently more mass, but diet treatments did not affect growth rate. We found no significant differences in quantitative lipid content or rates of CWL between diet treatments. An analysis for qualitative lipid content using infrared spectrophotometry also showed no diet effect, thus suggesting that lipid content and CWL are strong species-specific physiological performance traits not influenced by recent dietary history. While there is some evidence that epidermal permeability may be variable under certain environmental conditions (e.g., humidity), our findings show that diet has no effect and that a shift in prey preference may not influence or enhance physiological performance for decreasing CWL.

Comparison of central laboratory assessments of ER, PR, HER2, and Ki67 by IHC/FISH and the corresponding mRNAs (ESR1, PGR, ERBB2, and MKi67) by RT-qPCR on an automated, broadly deployed diagnostic platform

Purpose

The methods (IHC/FISH) typically used to assess ER, PR, HER2, and Ki67 in FFPE specimens from breast cancer patients are difficult to set up, perform, and standardize for use in low and middle-income countries. Use of an automated diagnostic platform (GeneXpert®) and assay (Xpert® Breast Cancer STRAT4) that employs RT-qPCR to quantitate ESR1, PGR, ERBB2, and MKi67 mRNAs from formalin-fixed, paraffin-embedded (FFPE) tissues facilitates analyses in less than 3 h. This study compares breast cancer biomarker analyses using an RT-qPCR-based platform with analyses using standard IHC and FISH for assessment of the same biomarkers.

Methods

FFPE tissue sections from 523 patients were sent to a College of American Pathologists-certified central reference laboratory to evaluate concordance between IHC/FISH and STRAT4 using the laboratory’s standard of care methods. A subset of 155 FFPE specimens was tested for concordance with STRAT4 using different IHC antibodies and scoring methods.

Results

Concordance between STRAT4 and IHC was 97.8% for ESR1, 90.4% for PGR, 93.3% for ERBB2 (IHC/FISH for HER2), and 78.6% for MKi67. Receiver operating characteristic curve (ROC) area under the curve (AUC) values of 0.99, 0.95, 0.99, and 0.85 were generated for ESR1, PGR, ERBB2, and MKi67, respectively. Minor variabilities were observed depending on the IHC antibody comparator used.

Conclusion

Evaluation of breast cancer biomarker status by STRAT4 was highly concordant with central IHC/FISH in this blinded, retrospectively analyzed collection of samples. STRAT4 may provide a means to cost-effectively generate standardized diagnostic results for breast cancer patients in low- and middle-income countries.

Electronic supplementary material

The online version of this article (10.1007/s10549-018-4889-5) contains supplementary material, which is available to authorized users.

Abstract P1-03-03: High concordance of ER, PR, HER2 and Ki67 by central IHC and FISH with mRNA measurements by GeneXpert® breast cancer stratifier assay

Current methods for the assessment of ER, PR, Her2, and Ki67 using FFPE tissues are hard to standardize and difficult to perform in Low and Middle Income Countries (LMIC). The GeneXpert® breast cancer stratifier assay (RUO) (BC Strat) is a cartridge-based, RT-qPCR assay of ESR1, PGR, ERBB2, and MKi67 mRNAs using FFPE specimens. The assay is fast (&lt;2 hours, including &lt;10 minutes of hands-on time) and easy to perform.

The aims of this study were: 1) to evaluate the concordance of BC Strat using different IHC antibodies and scoring methods in a preliminary dataset (Part I); and 2) to assess concordance between BC Strat and high quality standard methods in an expanded dataset (Part II).

Methods

Part I: IHC Antibody Variability

To assess BC Strat concordance with various IHC antibodies, 155 invasive ductal carcinoma blocks were sourced from 3 sites. Twenty-four adjacent slide sections from each block were prepared and shipped to different labs for BC Strat analysis(Cepheid) or IHC and FISH testing. Table 1 summarizes the IHC antibodies and scoring methods used in each reference lab.

Table 1:IHC antibodies and scoring methods used in reference labs Antibody for IHClabIHC scoringERSP1MPLNAutomated (Aperio)ER6F11Path IncAutomated (Aperio)ER6F11USCManualPRIE2MPLNAutomated (Aperio)PR16Path IncAutomated (Aperio)PRPGR636USCManualHer2*4B5MPLNAutomated (Aperio)Her2*HercepTestUSCManualKi6730-9MPLNAutomated (Aperio)Ki67MIB1Path IncAutomated (Aperio)Ki67MIB1USCManual*HER2 FISH (all with PathVysion kit) was performed at USC

Part II: Concordance Study

522 invasive ductal carcinoma FFPE samples were sourced from 5 sites. All BC Strat analysis was performed at Cepheid and all IHC and FISH was performed in the Press laboratory at USC. Overall percent agreement (OPA), positive percent agreement (PPA), and negative percent agreement (NPA) between BC Strat and IHC were determined.

Results

Part I: IHC Antibody Variability

Table 2 summarizes the OPA for BC Strat analysis and IHC performed with different IHC antibodies and scoring methods. Slightly better concordance for ER and PR was observed between the BC Strat and the IHC methods performed at USC. Discordant IHC results were also observed among the reference labs' standard methodologies.

Table 2: Overall Percent Agreement between IHC and BC Strat Reference LabOPA with BC StratERMPLN92%ERPath Inc96%ERUSC98%PRMPLN84%PRPath Inc83%PRUSC87%Her2*MPLN*93%Her2*USC*91%Ki67MPLN75%Ki67Path Inc67%Ki67USC81%*for IHC 2+(equivocal), FISH HER2/CEP17 ratio was examined

Part II: Concordance Study

Of the 522 samples tested, 499 (96%) yielded valid results for both BC Strat and IHC (IHC and FISH for Her2). OPA between BC Strat and IHC was 98% for ESR1, 91% for PGR, 93% for ERBB2 (IHC and FISH, 97% for Her2 IHC excluding IHC2+), and 81% for MKi67.

Conclusion

BC Strat assay measurements for ESR1, PGR, ERBB2 and MKi67 mRNA expression in FFPE breast tumor tissues are highly concordant with IHC and FISH performed by high quality reference labs. Further investigations using clinical outcomes from independent studies including prospective-retrospective clinical trials are in progress.

Citation Format: Wu NC, Wong W, Ho KE, Chu VC, Rizo A, Davonport S, Kelly D, Makar R, Jassem J, Duchnowska R, Biernat W, Radecka B, Fujita T, Klein JL, Stonecypher M, Ohta S, Juhl H, Weidler JM, Bates M, Press MF. High concordance of ER, PR, HER2 and Ki67 by central IHC and FISH with mRNA measurements by GeneXpert® breast cancer stratifier assay [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 P1-03-03.

Abstract P1-03-11: Analytical validation for the RT-qPCR based multiplex mRNA measurements of ER, PgR, HER2, and Ki67 from FFPE tumor tissue using the GeneXpert breast cancer stratifier assay

BACKGROUND: Accurate assessment of ER, PgR, HER2 and Ki67 status is crucial for breast cancer therapy and patient management. Immunohistochemistry (IHC) assays have been standard diagnostic tools but they are complex and time-consuming to perform and may not be readily available in decentralized laboratories, particularly in low-to-middle income countries. Molecular diagnostics can be a sensitive and accurate alternative to the traditional IHC, and the GeneXpert Breast Cancer Stratifier assay RUO (BC Strat), a single use cartridge-based assay performed on the broadly distributed GeneXpert® Instrument (GX) platform, streamlines a technically demanding RT-qPCR process to provide easy, robust, and reproducible ESR1, PGR, ERBB2, and MKi67 mRNA measurements from a 4 µm thick, formalin-fixed paraffin embedded (FFPE) breast tumor section in less than 2 hours.

METHODS: Analytical validation of the BC Strat assay included studies of Linearity/Dynamic Range, Analytical Sensitivity (Minimum Assay Input), Specificity (Potential Interfering Substances), Carryover Contaminations, and Kit and Specimen Slide Stabilities. Both in-vitro RNA transcript (IVT) and/or clinical breast cancer tissues were used as sample input materials. Assay results for each analyte were generated from cycle threshold (Ct) values, and final positive/negative test results for each target were also reported as delta Ct values, where dCt = Ct [CYFIP1 Reference] – Ct [Target], using dCt cutoffs previously derived from a clinical sample cohort.

RESULTS: The BC Strat assay demonstrated ≥3 log Linear Dynamic Range covering 5-7 logs sample input for all 4 Target dCts with R2≥0.95 independently. The assay currently requires minimal sample input equivalent to CYFIP1 Ct≤35 (Ct=33.5 ±1.5Ct SD) from 20 replicates of 5-level serial sample dilutions using two independent assay lot materials. It is acceptably robust against non-tumor tissues, DCIS, necrotic and/or hemorrhagic cells, lymphocytes, and genomic DNA contaminants. No carryover contamination from the same GeneXpert module was observed over 20 repeat tests during 9 consecutive days. Current real-time data supports assay stability at 5, 30, 37, 45 and 50°C for at least 3 months with minimal performance impact. Sectioned FFPE breast tumor tissues generated consistent dCt results when stored at 4°C and 30°C for up to 1 month before BC Strat assay testing.

CONCLUSIONS: The analytical validations of the BC Strat assay demonstrate an easy and robust mRNA detection with high sensitivity, specificity, reproducibility, and stability in order to aid medical pathologists and clinicians to more rapidly and objectively determine ESR1, PGR, ERBB2, and MKi67 mRNA status in breast cancer. Although stability studies out to 37 months are ongoing, current data suggest the assay is stable for at least 3 months over a wide range of temperatures. The GeneXpert Breast Cancer Stratifier assay potentially offers a rapid, standardized, and cost-effective solution to streamlining complex molecular diagnostics available for use in local pathology laboratories worldwide.

Citation Format: Chu VC, Wu N, Ho KE, Rizo A, Malek M, Weidler JM, Bates M, Wong W. Analytical validation for the RT-qPCR based multiplex mRNA measurements of ER, PgR, HER2, and Ki67 from FFPE tumor tissue using the GeneXpert breast cancer stratifier assay [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 P1-03-11.

Abstract P1-03-07: High concordance of a closed system, near point of care, RT-qPCR breast cancer assay for HER2 (ERBB2) mRNA compared to both IHC/FISH and quantitative immunofluorescence

Background

Reliable assessment of HER2 receptor status in breast cancer by either IHC or FISH does not unequivocally define receptor expression, due to their semi-quantitative nature, and as many as 10-15% of cases fall into the ASCO/CAP “equivocal” category. Historically, RNA measurements by PCR, including using several commercially available platforms, have been tested, but have not gained broad acceptance for assessment of HER2. However, RNA measurement, as a continuous value, has potential for use for adjudication of the equivocal category. In the current study, we used a real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) assay (GeneXpert® Breast Cancer Stratifier RUO Assay, Cepheid, Sunnyvale, CA, USA) for ERBB2 (HER2) mRNA on the GeneXpert® (GX) platform (Cepheid), which utilizes a closed-system, single-use cartridge, automated system. The RT-qPCR results from GX were then compared with results from clinical HER2 IHC/FISH assays following ASCO/CAP 2013 HER2 testing guidelines (Wolff et al JCO 2013) and quantitative immunofluorescence (QIF).

Methods

Multiple cores (1mm in diameter) were retrospectively collected from 80 formalin-fixed paraffin-embedded (FFPE) tissue blocks with invasive breast cancer seen by Yale Pathology Labs between 1998 and 2011. Tissue cores were processed as lysates for testing at Yale in the automated GX assay. Briefly, gene-specific reverse transcription was performed, followed by RT-qPCR (TaqMan) and ERBB2 mRNA results were expressed as the difference in cycle threshold values (delta Ct) between the endogenous control transcript (CYFIP1) and the ERBB2 mRNA transcript. Results from IHC and FISH were extracted from the pathology reports for the Yale CLIA lab and QIF for each case was measured as previously described (Carvajal et al, JNCI 2015).

Results

Quality control testing showed that the GX platform shows no case to case cross contamination on material from routine histology practices. Concordance between RT-qPCR and IHC/FISH was 91.25% (sensitivity = 0.87; specificity = 0.94; PPV = 0.89; NPV = 0.92) using a pre-defined delta Ct cut-off (dCt ≥ -1) for HER2 (+) based on prior concordance studies with HER2 IHC/FISH. Concordance between RT-qPCR and QIF was 99% (sensitivity = 0.97; specificity = 1.0; PPV = 1.0; NPV = 0.98) using dCt ≥ -1 and the pre-defined cut-point for positivity by QIF.

Conclusions

The GX closed system RT-qPCR assay shows greater than 90% concordance with the ASCO/CAP 2013 HER2 IHC/FISH scoring. Additionally, the GX RT-qPCR assay is highly concordant (99%) with the continuous variable HER2 QIF assay, and may better reflect the true continuum of HER2 receptor status in invasive breast cancer. These initial results suggest that rapid, closed system molecular assays may have future value for the adjudication of the ASCO/CAP HER2 equivocal category. This pilot study did not include ASCO/CAP 2013 “equivocal” cases, but that effort is underway.

Citation Format: Wasserman B, Carvajal-Hausdorf D, Ho K, Wong W, Wu N, Chu VC, Lai EW, Weidler JM, Bates M, Neumenister V, Rimm DL. High concordance of a closed system, near point of care, RT-qPCR breast cancer assay for HER2 (ERBB2) mRNA compared to both IHC/FISH and quantitative immunofluorescence [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 P1-03-07.

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&lt;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.

Quantitative HER2 and p95HER2 levels in primary breast cancers and matched brain metastases

BACKGROUND

Patients with advanced breast cancer positive for human epidermal growth factor receptor 2 (HER2) are at high risk for brain metastasis (BM). The prevalence and significance of expression of HER2 and its truncated form p95HER2 (p95) in BM is unknown.

METHODS

Seventy-five pairs of formalin-fixed paraffin-embedded samples from matched primary breast cancers (PBCs) and BM were assayed for quantitative p95 and HER2-total (H2T) protein expression using the p95 VeraTag and HERmark assays, respectively.

RESULTS

There was a net increase in p95 and H2T expression in BM relative to the matched PBC (median 1.5-fold, P = .0007 and 2.1-fold, P < .0001, respectively). Cases with H2T-positive tumors were more likely to have the largest (≥5-fold) increase in p95 (odds ratio = 6.3, P = .018). P95 positivity in PBC correlated with progression-free survival (hazard ratio [HR] = 2.2, P = .013), trended with shorter time to BM (HR = 1.8, P = .070), and correlated with overall survival (HR = 2.1, P = .042). P95 positivity in BM correlated with time to BM (HR = 2.0, P = .016) but did not correlate with overall survival from the time of BM diagnosis (HR = 1.2, P = .61).

CONCLUSIONS

This is the first study of quantitative p95 and HER2 expression in matched PBC and BM. BM of breast cancer shows significant increases in expression of both biomarkers compared with matched PBC. These data provide a rationale for future correlative studies on p95 and HER2 levels in BM.

HER3, p95HER2, and HER2 protein expression levels define multiple subtypes of HER2-positive metastatic breast cancer

Trastuzumab is effective in the treatment of HER2/neu over-expressing breast cancer, but not all patients benefit from it. In vitro data suggest a role for HER3 in the initiation of signaling activity involving the AKT–mTOR pathway leading to trastuzumab insensitivity. We sought to investigate the potential of HER3 alone and in the context of p95HER2 (p95), a trastuzumab resistance marker, as biomarkers of trastuzumab escape. Using the VeraTag® assay platform, we developed a dual antibody proximity-based assay for the precise quantitation of HER3 total protein (H3T) from formalin-fixed paraffin-embedded (FFPE) breast tumors. We then measured H3T in 89 patients with metastatic breast cancer treated with trastuzumab-based therapy, and correlated the results with progression-free survival and overall survival using Kaplan–Meier and decision tree analyses that also included HER2 total (H2T) and p95 expression levels. Within the sub-population of patients that over-expressed HER2, high levels of HER3 and/or p95 protein expression were significantly associated with poor clinical outcomes on trastuzumab-based therapy. Based on quantitative H3T, p95, and H2T measurements, multiple subtypes of HER2-positive breast cancer were identified that differ in their outcome following trastuzumab therapy. These data suggest that HER3 and p95 are informative biomarkers of clinical outcomes on trastuzumab therapy, and that multiple subtypes of HER2-positive breast cancer may be defined by quantitative measurements of H3T, p95, and H2T.

Quantitative measurements of tumoral p95HER2 protein expression in metastatic breast cancer patients treated with trastuzumab: independent validation of the p95HER2 clinical cutoff

PURPOSE

P95HER2 (p95) is a truncated form of the HER2, which lacks the trastuzumab-binding site and contains a hyperactive kinase domain. Previously, an optimal clinical cutoff of p95 expression for progression-free survival (PFS) and overall survival (OS) was defined using a quantitative VeraTag assay (Monogram Biosciences) in a training set of trastuzumab-treated metastatic breast cancer (MBC) patients.

EXPERIMENTAL DESIGN

In the current study, the predictive value of the p95 VeraTag assay cutoff established in the training set was retrospectively validated for PFS and OS in an independent series of 240 trastuzumab-treated MBC patients from multiple institutions.

RESULTS

In the subset of 190 tumors assessed as HER2-total (H2T)-positive using the quantitative HERmark assay (Monogram Biosciences), p95 VeraTag values above the predefined cutoff correlated with shorter PFS (HR = 1.43; P = 0.039) and shorter OS (HR = 1.94; P = 0.0055) where both outcomes were stratified by hormone receptor status and tumor grade. High p95 expression correlated with shorter PFS (HR = 2.41; P = 0.0003) and OS (HR = 2.57; P = 0.0025) in the hormone receptor-positive subgroup of patients (N = 78), but not in the hormone receptor-negative group. In contrast with the quantitative p95 VeraTag measurements, p95 immunohistochemical expression using the same antibody was not significantly correlated with outcomes.

CONCLUSIONS

The consistency in the p95 VeraTag cutoff across different cohorts of patients with MBC treated with trastuzumab justifies additional studies using blinded analyses in larger series of patients.

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.

Prevalence of Primary HIV‐1 Drug Resistance among Recently Infected Adolescents: A Multicenter Adolescent Medicine Trials Network for HIV/AIDS Interventions Study

This study examined the prevalence of primary human immunodeficiency type 1 (HIV-1) drug resistance among recently infected youth in the United States. Of the 55 subjects studied, major mutations conferring HIV drug resistance were present in 10 (18%). Eight (15%) had nonnucleoside reverse-transcriptase inhibitor (NNRTI) mutations, with the majority (6) having the K103N mutation; 2 (4%) had nucleoside reverse-transcriptase inhibitor (NRTI) mutations; and 2 (4%) had protease inhibitor (PI) mutations. Phenotypic drug resistance was present in 12 (22%) subjects: 10 (18%) for NNRTIs, 2 (4%) for NRTIs, and 3 (5.5%) for PIs. The prevalence of primary HIV-1 drug resistance, particularly to NNRTIs, in this group of recently infected youth was high.