Analytical validation of HER2DX genomic test for early-stage HER2-positive breast cancer

BACKGROUND

HER2DX, a multianalyte genomic test, has been clinically validated to predict breast cancer recurrence risk (relapse risk score), the probability of achieving pathological complete response post-neoadjuvant therapy (pCR likelihood score), and individual ERBB2 messenger RNA (mRNA) expression levels in patients with early-stage human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This study delves into the comprehensive analysis of HER2DX's analytical performance.

MATERIALS AND METHODS

Precision and reproducibility of HER2DX risk, pCR, and ERBB2 mRNA scores were assessed within and between laboratories using formalin-fixed paraffin-embedded (FFPE) tumor tissues and purified RNA. Robustness was appraised by analyzing the impact of tumor cell content and protocol variations including different instruments, reagent lots, and different RNA extraction kits. Variability was evaluated across intratumor biopsies and genomic platforms [RNA sequencing (RNAseq) versus nCounter], and according to protocol variations.

RESULTS

Precision analysis of 10 FFPE tumor samples yielded a maximal standard error of 0.94 across HER2DX scores (1-99 scale). High reproducibility of HER2DX scores across 29 FFPE tumors and 20 RNAs between laboratories was evident (correlation coefficients >0.98). The probability of identifying score differences >5 units was ≤5.2%. No significant variability emerged based on platform instruments, reagent lots, RNA extraction kits, or TagSet thaw/freeze cycles. Moreover, HER2DX displayed robustness at low tumor cell content (10%). Intratumor variability across 212 biopsies (106 tumors) was <4.0%. Concordance between HER2DX scores from 30 RNAs on RNAseq and nCounter platforms exceeded 90.0% (Cohen's κ coefficients >0.80).

CONCLUSIONS

The HER2DX assay is highly reproducible and robust for the quantification of recurrence risk, pCR likelihood, and ERBB2 mRNA expression in early-stage HER2-positive breast cancer.

Association of HER2DX with pathological complete response and survival outcomes in HER2-positive breast cancer

BACKGROUND

The HER2DX genomic test predicts pathological complete response (pCR) and survival outcome in early-stage HER2-positive (HER2+) breast cancer. Here, we evaluated the association of HER2DX scores with (i) pCR according to hormone receptor status and various treatment regimens, and (ii) survival outcome according to pCR status.

MATERIALS AND METHODS

Seven neoadjuvant cohorts with HER2DX and clinical individual patient data were evaluated (DAPHNe, GOM-HGUGM-2018-05, CALGB-40601, ISPY-2, BiOnHER, NEOHER and PAMELA). All patients were treated with neoadjuvant trastuzumab (n = 765) in combination with pertuzumab (n = 328), lapatinib (n = 187) or without a second anti-HER2 drug (n = 250). Event-free survival (EFS) and overall survival (OS) outcomes were available in a combined series of 268 patients (i.e. NEOHER and PAMELA) with a pCR (n = 118) and without a pCR (n = 150). Cox models were adjusted to evaluate whether HER2DX can identify patients with low or high risk beyond pCR status.

RESULTS

HER2DX pCR score was significantly associated with pCR in all patients [odds ratio (OR) per 10-unit increase = 1.59, 95% confidence interval 1.43-1.77; area under the ROC curve = 0.75], with or without dual HER2 blockade. A statistically significant increase in pCR rate due to dual HER2 blockade over trastuzumab-only was observed in HER2DX pCR-high tumors treated with chemotherapy (OR = 2.36 (1.09-5.42). A statistically significant increase in pCR rate due to multi-agent chemotherapy over a single taxane was observed in HER2DX pCR-medium tumors treated with dual HER2 blockade (OR = 3.11, 1.54-6.49). The pCR rates in HER2DX pCR-low tumors were ≤30.0% regardless of treatment administered. After adjusting by pCR status, patients identified as HER2DX low-risk had better EFS (P < 0.001) and OS (P = 0.006) compared with patients with HER2DX high-risk.

CONCLUSIONS

HER2DX pCR score and risk score might help identify ideal candidates to receive neoadjuvant dual HER2 blockade in combination with a single taxane in early-stage HER2+ breast cancer.

A phase Ib study of pembrolizumab (pembro) plus trastuzumab emtansine (T-DM1) for metastatic HER2+ breast cancer (MBC)

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Background: Preclinical evidence suggests treatment (tx) with T-DM1 plus an anti-PD1 antibody triggers antitumor immunity. We conducted a phase 1 trial to determine the safety and explore the efficacy of T-DM1 plus pembro. Methods: Eligible patients (pts) had MBC previously treated with trastuzumab (H) and taxane (T), were T-DM1-naïve, and received >1 prior line of tx for MBC or developed recurrence within 6 months (mo) of adjuvant tx. A dose de-escalation (esc) design was used with 6 pts in the dose-finding cohort, followed by an expansion (exp) cohort at the recommended phase 2 dose (RP2D), with mandatory baseline biopsies (bx). The primary endpoint was safety and tolerability. Secondary endpoints included objective response rate (ORR), progression-free survival (PFS), and clinical benefit rate (CBR: complete response + partial response + stable disease >24 weeks). Associations between immune biomarkers and tx response were explored. Results: 20 pts started protocol tx (6 in dose de-esc cohort; 14 in exp cohort). Median follow-up was 23.5 mo. Pts had median age 54 yrs and median 1 line of prior MBC tx (range 0-2); 100% had received prior T, H, and pertuzumab. There were no dose-limiting toxicities in the dose de-esc cohort; thus full doses of T-DM1 (3.6 mg/kg q21 days) and pembro (200 mg q21 days) were the RP2D. 85% of pts experienced tx-related adverse events (AEs) > grade (gr) 1; 20% of pts experienced gr3 AEs. There were no gr>4 AEs. Gr3 AEs were fatigue; AST increase; ALT increase; pneumonia; pneumonitis; oral mucositis; and vomiting, each in 1 pt. 17 pts had baseline bx; 6 pts had repeat bx after 1 tx cycle. Efficacy results, overall and by PD-L1 Combined Positive Score (CPS; 22C3 staining) and tumor-infiltrating lymphocyte (TIL) status, are shown in the table. Tumors’ antigen presentation will be explored through HLA/dendritic cell marker staining and immune signatures by RNA sequencing. Conclusions: T-DM1 plus pembro was safe and tolerable. The regimen demonstrated clinical activity. Further exploration of immune-related predictive biomarkers is warranted. Clinical trial information: NCT03032107 . [Table: see text]

Reversion and non-reversion mechanisms of resistance to PARP inhibitor or platinum chemotherapy in BRCA1/2-mutant metastatic breast cancer

BACKGROUND

Little is known about mechanisms of resistance to poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) and platinum chemotherapy in patients with metastatic breast cancer and BRCA1/2 mutations. Further investigation of resistance in clinical cohorts may point to strategies to prevent or overcome treatment failure.

PATIENTS AND METHODS

We obtained tumor biopsies from metastatic breast cancer patients with BRCA1/2 deficiency before and after acquired resistance to PARPi or platinum chemotherapy. Whole exome sequencing was carried out on each tumor, germline DNA, and circulating tumor DNA. Tumors underwent RNA sequencing, and immunohistochemical staining for RAD51 foci on tumor sections was carried out for functional assessment of intact homologous recombination (HR).

RESULTS

Pre- and post-resistance tumor samples were sequenced from eight patients (four with BRCA1 and four with BRCA2 mutation; four treated with PARPi and four with platinum). Following disease progression on DNA-damaging therapy, four patients (50%) acquired at least one somatic reversion alteration likely to result in functional BRCA1/2 protein detected by tumor or circulating tumor DNA sequencing. Two patients with germline BRCA1 deficiency acquired genomic alterations anticipated to restore HR through increased DNA end resection: loss of TP53BP1 in one patient and amplification of MRE11A in another. RAD51 foci were acquired post-resistance in all patients with genomic reversion, consistent with reconstitution of HR. All patients whose tumors demonstrated RAD51 foci post-resistance were intrinsically resistant to subsequent lines of DNA-damaging therapy.

CONCLUSIONS

Genomic reversion in BRCA1/2 was the most commonly observed mechanism of resistance, occurring in four of eight patients. Novel sequence alterations leading to increased DNA end resection were seen in two patients, and may be targetable for therapeutic benefit. The presence of RAD51 foci by immunohistochemistry was consistent with BRCA1/2 protein functional status from genomic data and predicted response to later DNA-damaging therapy, supporting RAD51 focus formation as a clinically useful biomarker.

A phase II feasibility study of palbociclib in combination with adjuvant endocrine therapy for hormone receptor-positive invasive breast carcinoma

BACKGROUND

The CDK4/6 inhibitor palbociclib prolongs progression-free survival in hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer when combined with endocrine therapy. This phase II trial was designed to determine the feasibility of adjuvant palbociclib and endocrine therapy for early breast cancer.

PATIENTS AND METHODS

Eligible patients with HR+/HER2- stage II-III breast cancer received 2 years of palbociclib at 125 mg daily, 3 weeks on/1 week off, with endocrine therapy. The primary end point was discontinuation from palbociclib due to toxicity, non-adherence, or events related to tolerability. A discontinuation rate of 48% or higher would indicate the treatment duration of 2 years was not feasible, and was evaluated under a binomial test using a one-sided α = 0.025.

RESULTS

Overall, 162 patients initiated palbociclib; over half had stage III disease (52%) and most received prior chemotherapy (80%). A total of 102 patients (63%) completed 2 years of palbociclib; 50 patients discontinued early for protocol-related reasons (31%, 95% CI 24% to 39%, P = 0.001), and 10 discontinued due to protocol-unrelated reasons. The cumulative incidence of protocol-related discontinuation was 21% (95% CI 14% to 27%) at 12 months from start of treatment. Rates of palbociclib-related toxicity were congruent with the metastatic experience, and there were no cases of febrile neutropenia. Ninety-one patients (56%) required at least one dose reduction.

CONCLUSION

Adjuvant palbociclib is feasible in early breast cancer, with a high proportion of patients able to complete 2 years of therapy. The safety profile in the adjuvant setting mirrors that observed in metastatic disease, with approximately half of the patients requiring dose-modification. As extended duration adjuvant palbociclib appears feasible and tolerable for most patients, randomized phase III trials are evaluating clinical benefit in this population.

CLINICALTRIALS.GOV REGISTRATION

NCT02040857.

Reversion and non-reversion mechanisms of resistance (MoR) to PARP inhibitor (PARPi) or platinum chemotherapy (chemotx) in patients (pts) with BRCA1/2-mutant metastatic breast cancer (MBC)

1085

Background: Little is known about MoR to PARPi and platinum chemotx in MBC pts with BRCA1/2 mutations. Biomarkers predictive of response/resistance have not been identified, but could have clinical utility. Methods: We obtained 8 BRCA-mutant metastatic tumor biopsies from MBC pts with acquired resistance to DNA-damaging tx (PARPi/platinum) on a prospective tissue collection protocol. In 7/8 patients, we also obtained pre-tx biopsies. Whole exome sequencing (WES) was performed on each tumor and on germline DNA from blood. We performed immunohistochemical (IHC) staining for RAD51 foci for functional assessment of intact homologous recombination (HR). Results: 4/7 pts with complete WES analysis acquired a somatic reversion mutation likely to result in functional BRCA1/2 protein in the post-tx tumor specimen after platinum (2 pts) or PARPi (2 pts; Table). 4/7 pts had plausible non-reversion MoR identified by WES, including alterations in genes involved in replication fork protection and DNA end resection. As expected, in all pts with genomic reversion, RAD51 foci were acquired in the post-resistance tumor, consistent with reconstitution of HR. In 2 pts without reversion, presence of RAD51 foci post-resistance was mixed. Reversion mutations occurred both with and without other alterations that could possibly lead to fork protection, suggesting > 1 MoR could occur in the same tumor. 3 pts whose tumors demonstrated RAD51 foci post-resistance were later re-exposed to DNA-damaging tx, to which all had intrinsic resistance. Conclusions: BRCA1/2 reversion was identified as a MoR in the majority of pts. WES identified potential novel MoR in fork protection and end resection genes. The presence of RAD51 foci by IHC was consistent with BRCA protein functional status from genomic data and predicted response to later DNA-damaging tx, suggesting RAD51 IHC may be a clinically useful biomarker. [Table: see text]

Avoiding peg-filgrastim (Peg-F) prophylaxis during the paclitaxel (T) portion of the dose-dense (DD) doxorubicin-cyclophosphamide (AC)-T regimen: A prospective study

517

Background: Use of growth factors (GF) adds considerable expense and some toxicity to adjuvant breast cancer chemotherapy. We tested the feasibility and safety of omitting routine GF use during the T portion of DD AC-T. Methods: This is a prospective, single-arm study in which patients (pts) who completed 4 cycles of DD-AC proceeded to DD-T 175 mg/m2 every two weeks (wks) without routine GF (NCT02698891). Key inclusion: age≤ 65, ECOG PS≤1, absolute neutrophil count (ANC) ≥1500/mm3, and no febrile neutropenia (FN) during DD-AC. Criteria to treat for T included ANC ≥1000/mm3. Peg-F was given only if pts had FN in a prior cycle, or at investigator discretion if infection or treatment delay > 1 wk. Once Peg-F was given, pts received it in all future cycles. The primary endpoint was the rate of T completion ≤ 7 wks from cycle 1 day 1 (C1D1) to C4D1. Secondary endpoints included total use of Peg-F, rates of hematologic toxicity and FN, reasons for dose modification or hold. If ≥85% of pts completed T on time, the regimen would be considered feasible. If the true on-time completion rate is 75%, the chance the regimen would be declared infeasible is 91%, and if it is 85% the chance that the regimen is falsely declared infeasible is 10% (power = 0.899). ≥100/125 pts had to complete T on time for the regimen to be deemed successful. Results: Among 127 pts enrolled, 125 received ≥1 dose of protocol therapy and are included in the analysis. Median age at registration was 46 (range 21-65). Median C1D1 ANC was 7500/mm3 (range 1500-20500). 112 (90%) (95% CI 83-94%) pts completed DD-T ≤ 7 wks, and 3 (2%) completed within > 7 wks (2 due to neutropenia); 10 (8%) did not complete all cycles of T. Omission of Peg-F was not causally related to non-completion of T in any pts. The most common reasons for dose reduction or delays were non-hematologic. One pt had FN but was able to complete T on time. Eight (6.4%) pts received Peg-F during the trial. Conclusions: Omission of routine GF use during DD-T according to a pre-specified algorithm appears safe, feasible, and was associated with a 95.7% reduction in use of Peg-F, relative to the current standard of care. Additional analyses including cost implications are ongoing. Clinical trial information: NCT02698891.

Genomics of HER2+ breast cancer in young women before and after exposure to chemotherapy (chemo) plus trastuzumab (H)

554

Background: HER2+ breast cancer (BC) is particularly common in young women. Genomic features of HER2+ tumors before and after H-based therapy have not been described in a population of young women and may point to clinically targetable mechanisms of resistance. Methods: From a large prospective cohort of women diagnosed with BC age ≤40 years, we identified those with HER2+ BC and tumor tissue available for sequencing before and after chemo+H. Whole exome sequencing (WES) was performed on each tumor and on germline DNA from blood. Tumor-normal pairs were analyzed for mutations and copy number (CN) changes. Evolutionary analysis was performed for patients with both pre- and post-treatment (tx) samples. Results: 22 women had successful WES samples from at least one timepoint; 13 of these had paired sequencing results both before and after chemo+H. For the majority of women, post-tx sample was following neoadjuvant chemo + H, though post-tx timepoint for other women represented locoregional or distant metastasis (Table). TP53 was the only gene that was significantly recurrently mutated in both pre- and post-tx samples. Comparison of matched pre-tx and post-tx samples demonstrated that large changes in HER2 CN over the course of tx were uncommon, only 2/13 pts had > 2-fold change in HER2 CN. Other clonal and subclonal genomic alterations were found to be acquired in the post-tx sample compared to the pre-tx sample. One patient acquired a putative activating mutation in ERBB2. Another patient acquired a clonal hotpsot mutation in TP53. MYC gene amplification was observed in 4 post-tx tumors. NOTCH2 alterations were found in post-tx biopsies from 2 different patients, and mutations in STIL were also found in post-tx biopsies from 2 patients, though the function of these mutations is not known. Conclusions: HER2+ breast tumors in young women display genomic evolution following tx with chemo+H. HER2 CN changes are uncommon, but we identified several genes that warrant exploration as potential mechanisms of resistance to therapy in this population.[Table: see text]

HER2 heterogeneity as a predictor of response to neoadjuvant T-DM1 plus pertuzumab: Results from a prospective clinical trial

502

Background: HER2 targeted therapy without chemotherapy may be insufficient to completely eradicate a HER2+ cancer in cases of significant intratumor HER2 heterogeneity (ITH-HER2). Methods: We conducted a single-arm phase II study enrolling centrally confirmed HER2+ breast cancer. Pts received 6 cycles of T-DM1 plus Pertuzumab before surgery. Central ITH-HER2 was assessed on baseline ultrasound-guided core biopsies from 2 distinct areas of each tumor (3 cores/site). ITH-HER2 was defined as at least one of the six areas demonstrating either 1) HER2 positivity by FISH in > 5% and < 50% of tumor cells (i.e., CAP guideline) or 2) an area of tumor that tested HER2 negative. The primary objective is the association between pathologic complete response (pCR) and ITH, stratified by ER status. pCR defined as residual cancer burden (RCB) 0. Results: 164 pts with centrally confirmed HER2+ tumors were enrolled from 1/2015 to 1/2018. 2 pts withdrew consent. Median tumor size by imaging was 2.8 cm (IQR 2.1-3.8cm); 111 (69%) were ER+ and 51 (32%) ER-. 8 pts discontinued tx (6 due to disease progression, 2 due to toxicity). 49% of pts had a pCR (RCB-0), 14% RCB-I, 26% RCB-II and 11% RCB-III. Higher rates of RCB-0 were seen in ER- (65%) versus ER+ (42%). ITH-HER2 was detected in 10% (16/157) of evaluable cases. No pCR was observed among cases classified as heterogeneous (RCB-I 25%, RCB-II 25%, RCB-III 50%). The study met its primary endpoint by demonstrating a significant association between ITH-HER2 and pCR stratified by ER status (p < .0001). Secondary analysis also demonstrated a significant association between ITH-HER2 and pathologic response defined as RCB 0 or I (OR = 5.6, p = 0.004). Exploratory analysis revealed higher rates of RCB-0 among tumors centrally classified as HER2 3+ (56% [66/118]) versus HER2 2+ (27% [10/37]), (OR = 3.4, p = 0.002). The association of ITH-HER2 and pCR was maintained when stratifying by ER status and HER2 IHC (2+ vs. 3+), (p = 0.002). Conclusions: ITH-HER2 assessed by routine pathology evaluation is a strong predictor of pCR to a dual-HER2 targeted therapy regimen. If validated, ITH-HER2 may need to be considered in selection of pts for HER2-targeted regimens without chemotherapy in the curative setting. Clinical trial information: NCT02326974.

Abstract PD6-09: The immune microenvironment in hormone receptor-positive breast cancer patients and relationship to treatment outcome following preoperative chemotherapy plus bevacizumab

Background: Hormone receptor-positive (HR+) tumors have fewer tumor-infiltrating lymphocytes (TILs) and lower response rates to immune checkpoint inhibitors (ICI), either as single agents or in combination with chemotherapy, than triple negative cancers. However, some HR+ cancers do respond to ICI and biomarkers that accurately reflect the immune microenvironment may help guide the use of ICI therapy. Prior evidence suggests that macrophage-related immune pathways may be relevant to the pathophysiology of HR+ BC.

Methods: HR+/HER2- patients were identified from a prospective trial of preoperative bevacizumab (preop bev) followed by bev with adriamycin/cyclophosphamide/paclitaxel dose-dense chemotherapy (chemo). Tumor samples were collected at diagnosis and surgery (pre-tx and post-tx), and PD-L1 expression (by immunohistochemistry), TILs, and Nanostring PanCancer Immune Profiling Panel were evaluated on both pre-tx and post-tx specimens. Pre-tx whole transcriptome sequencing was performed. Pathologic response at surgery was centrally assessed by Miller-Payne (MP) and residual cancer burden (RCB) scores. An immune score was calculated for each pre-tx specimen by integrating 10 published immune signatures. Immune cell subsets were inferred from bulk transcriptional data using CIBERSORT and immune cell-specific signatures from MSigDB.

Results: 55 patients who received trial therapy and had at least 1 evaluable specimen were included for analysis. Pre-tx TILs and tumor PD-L1 (tPD-L1) scores are shown in the table. 18% of pre-tx tumors had “high” (≥10%) TILs and “high” TILs were associated with significantly higher immune signature score (p=0.004). Immune score correlated highly with proportion of CIBERSORT anti-tumor M1 macrophages as well as CD8 T-cell signatures (r&gt;0.65 and p&lt;0.001). Higher pre-tx TILs, tPD-L1, or immune score were each significantly associated with more favorable RCB and MP in unadjusted analyses (all Spearman p&lt;0.01 for pathologic markers; ANOVA p&lt;0.04 for immune score). After adjustment for age and tumor grade, higher pre-tx TILs and tPD-L1 were associated with favorable RCB (p&lt;0.01 for both), and higher pre-tx tPD-L1 correlated with favorable MP (p=0.03). Pathologic complete response occurred in 4 pts; all 4 had high pre-tx TILs, pre-tx tPD-L1, or both. Among patients with residual disease, large changes (&gt;5%) in TILs or tPD-L1 from pre-tx to post-tx were rare: 2 pts each had large changes in TIL or tPD-L1 score (N=38/N=31 pairs, respectively).

Conclusions: High levels of tumor-lymphocyte interaction were seen in only a minority of untreated HR+ breast tumors, and did not typically change with chemo plus bev. An immune score derived from bulk RNAseq correlated with histological observations in these specimens. Nonetheless, TILs, tPD-L1, and signature-derived immune score were significantly associated with pathologic response to preop treatment in HR+ disease. Early data suggest that the role of M1 macrophages in HR+ tumors warrants further investigation.

ScoreTILs (N=50 evaluable)Tumor PD-L1 (N=51)0%0 pts (0%)28 pts (55%)&gt;0-5% (low)19 (38%)18 (35%)&gt;5-10% (intermediate)22 (44%)3 (6%)&gt;10% (high)9 (18%)2 (4%)

Citation Format: Waks AG, Stover DG, Barry W, Dillon D, Gjini E, Rodig SJ, Brock J, Baltay M, Savoie J, Winer EP, Krop I, Tolaney SM. The immune microenvironment in hormone receptor-positive breast cancer patients and relationship to treatment outcome following preoperative chemotherapy plus bevacizumab [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD6-09.

Abstract PD5-06: Adjuvant palbociclib plus endocrine therapy for hormone receptor positive/HER2 negative breast cancer: A phase II feasibility study

Background:

The CDK4/6 inhibitor palbociclib (P) combined with endocrine therapy (ET) prolongs progression-free survival in previously untreated and treated hormone receptor positive/HER2 negative (HR+/HER2-) metastatic breast cancer (MBC). The most common toxicity with P is neutropenia, typically non-cumulative and uncomplicated. Given observed benefits of P in metastatic BC, this single arm phase II trial was designed to determine the feasibility and toxicity of combination adjuvant P and ET for HR+/HER2- early BC (EBC).

Methods:

Eligible patients (pts) had HR+/HER2- stage II (not T2N0)-III EBC, with prior completion of 3-24 mo of ET (either AI or tamoxifen) without significant adverse events (AE). Pts received P at 125 mg daily, 3 wk on/1 wk off in a 28d cycle, plus continuous ET, for planned duration 2 yrs. Pts were removed from study for toxicity, non-adherence, or other events related to tolerability; pts who recurred or completed 2 yrs of therapy were censored for the primary endpoint. The primary objective was to evaluate the treatment discontinuation rate at 2 yrs; a rate of &gt;50%, would indicated a non-feasible treatment duration (null hypothesis). Discontinuation rates at 2 yrs are estimated by Kaplan Meier with 95% confidence bands. A sample size of 160 pts provided 92% power to reject the null hypothesis using a one-sided alpha = 0.025 if the true rate of discontinuation is &lt;33.3%, and accounting for a censoring rate of up to 20% over the 2 yrs. Secondary endpoints include toxicity, adherence, QOL, and pharmacogenomics.

Results:

Between 3/2014 and 11/2015, 162 pts initiated P; the majority had stage III EBC (52%) and received prior chemotherapy (63%). As of 05/2017, 120 (74%) have completed at least 1 yr of P + ET, and 50 (31%) have completed 2 yrs of P + ET. Early discontinuation of protocol treatment was reported for 59 pts (36%), including 49 events (30%) related to protocol-mandated (9%) and non-mandated (21%) tolerability. The cumulative rate of all discontinuations was 15.1% at 6 mos, 20.9% at 12 mos and 27.8% at 18 mos. Half of all non-mandated discontinuations occurred within the first 6 mos of initiation of therapy, and the rate decreased with greater provider and pt education. Median duration of pts still on treatment is 20 mos (inter-quartile range: 18 to 21 mos). The rate of grade 3/4 neutropenia was 77%, with 0 cases of febrile neutropenia. Other common all-grade P-related AE &gt; 20% included fatigue 65%, alopecia 25%, mucositis 24%, and anemia 24%. 32% of pts required one dose reduction, 16% required two. There have been 2 BC recurrence events and 1 chemotherapy-related AML. Updated data for the primary analysis of feasibility and tolerability, as well as pharmacogenomics, QOL, and adherence, will be presented.

Conclusions:

In this single arm phase II trial, the majority of pts have completed at least 1 year of adjuvant P + ET therapy, with no new toxicity signals. Non-protocol discontinuations have decreased with education. Updated results for the primary analysis will be presented. As in the MBC setting, extended duration palbociclib appears feasible and tolerable for most pts. The efficacy of 2 years of P and ET will be addressed by the phase III PALLAS trial (NCT NCT02513394).

Citation Format: Mayer EL, DeMichele AM, Guo H, Miller KD, Rugo HS, Schneider B, Waks AG, Come SE, Mulvey T, Huang Bartlett C, Koehler M, Barry W, Winer EP, Burstein HJ. Adjuvant palbociclib plus endocrine therapy for hormone receptor positive/HER2 negative breast cancer: A phase II feasibility study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD5-06.

Immune biomarkers and treatment (tx) outcome in hormone receptor-positive (HR+) breast cancer (BC) patients (pts) treated with preoperative chemotherapy (preop chemo) plus bevacizumab (bev)

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Background: Though preliminary study of the BC immune microenvironment suggests that HR+ tumors are less immune-active than other subtypes, immune biomarkers may have important clinical implications in HR+ BC pts. Methods: 78 HR+/HER2- BC pts were enrolled on a prospective trial of preop bev followed by bev with adriamycin/cyclophosphamide/paclitaxel dose-dense chemo. Tumor samples were collected at diagnosis and surgery (pre-tx and post-tx). PD-L1 expression (by immunohistochemistry) and tumor-infiltrating lymphocytes (TILs) were scored. Whole transcriptome sequencing and Nanostring PanCancer Immune Profiling Panel were performed. Pathologic response at surgery was assessed by Miller-Payne (MP) and residual cancer burden (RCB) scores. We calculated adjusted correlations by linear/logistic regression for RCB/dichotomized MP, respectively. Results: 55 pts who received trial tx and had >1 analyzable specimen are included. Pre-tx TILs and tumor PD-L1 (tPD-L1) scores (see table) were slightly positively correlated (Spearman rho 0.23, p=0.1). Large changes (>5%) in TILs or tPD-L1 from pre-tx to post-tx were rare: 2 pts each had large changes in TIL or tPD-L1 score (N=38 and N=31 pairs, respectively). Higher pre-tx TILs or tPD-L1 were significantly associated with more favorable RCB and MP (all Spearman p<0.01) in unadjusted analyses. After adjustment for age and tumor grade, higher pre-tx TILs and tPD-L1 were associated with more favorable RCB (p<0.01 for both), and higher pre-tx tPD-L1 correlated with more favorable MP (p=0.03). Pathologic complete response occurred in 4 pts; all 4 had high pre-tx TILs, pre-tx tPD-L1, or both. Analysis of immune-related RNA signatures is ongoing. Conclusions: High levels of tumor-immune interaction were seen in only a minority of untreated HR+ breast tumors, and did not typically change after tx with chemo plus bev. Nonetheless, TILs and tPD-L1 are significantly associated with pathologic response to preop tx in HR+ disease. [Table: see text]

Abstract P3-07-31: Immune activation signatures identify a subset of ER+ breast cancers with increased pathologic complete response to neoadjuvant chemotherapy

Background: Proliferation is the strongest predictor of response to neoadjuvant chemotherapy in estrogen receptor-positive (ER+) breast cancer. Evidence of immune activation has also been associated with improved response to neoadjuvant chemotherapy in breast cancer. We hypothesized that immune signatures may be associated with response independent of proliferation in ER+ breast cancers.

Approach: We compiled microarray expression data from breast cancer biopsies obtained prior to neoadjuvant chemotherapy on 465 ER-positive/HER2-negative patients by reported pathologic receptor status. We evaluated the association of 118 published gene expression signatures with response to neoadjuvant chemotherapy, based on study-defined pathologic complete response (pCR) versus residual disease (RD).

Results: Overall, 42 of 118 signatures were significantly associated with response to neoadjuvant chemotherapy in ER+ breast cancer (FDR-corrected p&lt;0.05, simple logistic regression). Of those signatures that achieved significance, 52% (22/42) of signatures were proliferation-associated based on correlation to the 11-gene PAM50 proliferation index (Pearson's R2&gt;0.30, p&lt;1e-10). Among signatures that were NOT proliferation-associated, 50% (10/20) were immune-related. Using unsupervised hierarchical clustering of all 118 signatures, these ten immune signatures formed a distinct cluster. Of the 10 signatures, nine were designed to reflect "immune activation" and were highly correlated with each other in ER+ tumors (R2&gt;0.4, p&lt;0.001). The mean of each of these nine signatures was significantly higher in patients with pCR versus RD (FDR-corrected p&lt;0.05, t-test). Patients with higher "immune activation" signatures had increased likelihood of pCR within multiple subgroups of ER+ breast cancer, including luminal B and non-luminal PAM50 subgroups, as well as intermediate- and high-proliferation ER+ breast cancers. For luminal A or low-proliferation breast cancers, "immune activation" signatures were not significantly associated with response, though very few patients achieved pCR in these two subgroups.

Conclusions: Gene expression signatures associated with "immune activation" identify a subset of ER+ breast cancers with higher rates of pCR to neoadjuvant chemotherapy. These "immune activation" signatures appear to be proliferation-independent and may provide additional predictive information to existing gene expression-based approaches for ER+ breast cancer.

Citation Format: Stover DG, Waks AG, Erica ML, Brugge JS, Winer EP, Selfors LM. Immune activation signatures identify a subset of ER+ breast cancers with increased pathologic complete response to neoadjuvant chemotherapy. [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 P3-07-31.