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Practice-Changing Data in Breast Cancer
Breast Cancer: A Look Ahead to Practice-Changing Data at the 2016 Clinical Oncology Meeting

Released: May 31, 2016

Expiration: May 30, 2017

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At this year’s ASCO annual meeting, several interesting studies in breast cancer are being reported, some of which may be practice changing. I will highlight some of these data with downloadable slidesets and an online activity where I will discuss the clinical implications of the data with Tiffany A. Traina, MD, after the ASCO annual meeting.

Hormone Receptor–Positive Disease
In the adjuvant setting, the results of the MA17R trial (LBA1), with patient-reported outcomes in LBA506, are eagerly anticipated as this is the first trial reporting data comparing 5 vs 10 years of aromatase inhibitor (AI) therapy. In this study, patients who completed 5 years of an adjuvant AI (either 5 years of standard adjuvant AI or 5 years of tamoxifen followed by 5 years of letrozole on the MA17 study) were randomized to an additional 5 years of letrozole (total of 10 years of AI) or placebo. Supported with data from the retrospective EBCTCG meta-analysis being presented in the same session (505) on long-term (14-year) risk of relapse for patients with estrogen receptor (ER)–positive early-stage breast cancer (N = 46,138), MA17R will address the highly relevant clinical question of whether the use of prolonged AI therapy improves the persistent risk of recurrence and has an acceptable toxicity profile.

In the metastatic hormone receptor–positive setting, the highly anticipated results of PALOMA-2, evaluating first-line letrozole plus the CDK4/6 inhibitor palbociclib are being presented (507). The PFS results from this placebo-controlled phase III study confirm those from the phase II (PALOMA-1) trial that led to the FDA accelerated approval of palbociclib in February 2015. Results from the phase II MONARCH1 study evaluating another CDK4/6 inhibitor, abemaciclib, as a single agent (510) are being presented as well.

HER2-Positive Disease
The first analysis of the phase III neoadjuvant KRISTINE (TRIO-021) trial, in which 6 cycles of standard chemotherapy—docetaxel/carboplatin—plus trastuzumab/pertuzumab (TCHP) are compared with a regimen that does not contain standard chemotherapy–ado-trastuzumab emtansine (T-DM1) plus pertuzumab—will be presented (500). Along the same lines, the WSG-ADAPT study (518), in which patients with hormone receptor–negative, HER2-positive breast cancer were treated with 12 weeks of trastuzumab/pertuzumab (HP) with or without paclitaxel will also be reported.

In the advanced disease setting, the phase III PHEREXA trial evaluating the addition of pertuzumab to capecitabine plus trastuzumab in patients who had been previously treated with trastuzumab-based therapy for metastatic disease will also be reported (504). This study will be the first phase III trial reported to address the effects of combination therapy with pertuzumab in the second-line setting.

Triple-Negative Disease; Immunotherapy and Chemotherapy
Interesting results from a phase II/III trial of a novel vaccine targeting Globo-H (OPT-822/OPT-821) in metastatic breast cancer will be reported (1003). Although PFS is similar in the treatment arms, patients who developed an immune response (especially those with triple-negative disease) appeared to have a significantly better outcome.

A critical question that is being addressed by several ongoing studies (eg, the German SUCCESS-C and WSG-PlanB) in early-stage HER2-negative breast cancer is whether or not anthracyclines add significant benefit to taxane-based therapy. An interim joint analysis of the Anthracyclines in early Breast Cancer (ABC) trials—3 separate phase III studies by US Oncology Research (USOR) and National Surgical Adjuvant Breast and Bowel Project (NSABP) comparing docetaxel/cyclophosphamide for 6 cycles with regimens of docetaxel or paclitaxel plus doxorubicin and cyclophosphamide in women with resected high-risk, HER2-negative breast cancer (N = 4242)—will be reported this year (1000). Related to this topic are 2 abstracts evaluating nonanthracycline-based chemotherapy for early-stage triple-negative breast cancer (1068) (1015).

Other Areas of Interest
Central Nervous System (CNS) Metastases
Several abstracts of interest will be reported that address treatment of CNS metastases, an area of unmet need in breast oncology. The following abstracts in particular are exciting: abstract 526 reports on levels of abemaciclib achieved in brain tissue of patients with CNS metastases; abstract 513 reports efficacy results in brain metastases from a phase Ib study evaluating ONT-380 (a tyrosine kinase inhibitor) plus T-DM1; abstract 514 reports on another CNS penetrant TKI, tesevatinib plus trastuzumab; and abstract 582 reports on activity of T-DM1 in the brain.

Interpreting HER2 and ER Results
Two abstracts of interest are being presented that call into question the current guidelines for interpreting HER2 and ER results. In abstract 515, analysis of 10,468 samples (all tested for HER2 by FISH) were reanalyzed by current ASCO/College of American Pathologists guidelines and assessed for correlations with HER2 protein, clinical outcomes and trastuzumab benefit. In abstract 1067, HER2-negative tumor samples (N = 3237) were assessed for ER to define the optimal cutoff value (< 1% vs < 10%) below which early-stage disease behaves like triple-negative breast cancer.

Final Thoughts
These studies being presented at 2016 ASCO will answer some important clinical questions for the optimal treatment of breast cancer. What results are you looking forward to seeing at the 2016 ASCO annual meeting?

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