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Management of Metastatic Breast Cancer

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Northeast Florida Medicine, Vol. 69, No. 4, October 2018

Progress in the Management of Metastatic Breast Cancer in 2018: Is a Cure in the Horizon?

Mayo Clinic, Florida

Address Correspondence to:

Gerardo Colón-Otero, MD
Professor of Medicine
Mayo Clinic Collge of Medicine
Vice-Dean Mayo Clinic School of Medicine
Dean, Florida Campus, Mayo Clinic School of Medicine
Phone: (904) 742-6002

Date of Release: October 1, 2018
Date Credit Expires: October 1, 2020
Estimated Completion Time: 1 hour

The Duval County Medical Society (DCMS) is proud to provide its members with free continuing medical education (CME) opportunities in subject areas mandated and suggested by the State of Florida Board of Medicine to obtain and retain medical licensure. The DCMS would like to thank the St. Vincent’s Healthcare Committee on CME for reviewing and accrediting this activity in compliance with the Accreditation Council on Continuing Medical Education (ACCME). This issue of Northeast Florida Medicine includes an article, “Progress in the management of metastatic breast cancer in 2018: Is a cure in the horizon?” authored by Gerardo Colón-Otero, MD, which has been approved for 1 AMA PRA Category 1 credit.TM For a full description of CME requirements for Florida physicians, please visit


Gerardo Colón-Otero, MD, Professor of Medicine, Mayo Clinic College of Medicine, Vice-Dean, Mayo Clinic School of Medicine, Dean, Florida Campus, Mayo Clinic School of Medicine.

Needs Assessment:

Multiple new drugs have been approved for the treatment of metastatic breast cancer over the last six years and multiple additional drugs are likely to become FDA approved over the next two years. There is a need for a review of the current status of these treatments. 


1. List the drugs approved over the last six years for the treatment of metastatic breast cancer.
2. Describe the biomarkers used for the selection of treatments for patients with metastatic breast cancer.
3. State the names of promising new drugs currently being evaluated for the management of metastatic breast cancer.

CME Credit Eligibility:

A minimum passing grade of 70% must be achieved. Only one re-take opportunity will be granted. If you take your test online, a certificate of credit/completion will be automatically downloaded to your DCMS member profile. If you submit your test by mail, a certificate of credit/completion will be emailed within 4 weeks of submission. If you have any questions, please contact Kristy Williford at 904-355-6561 or 

Faculty Disclosure:

Gerardo Colón-Otero, MD reports grant/research support from Novartis to Mayo Clinic for Investigator Initiated Trial.

Disclosure of Conflicts of Interest:

St. Vincent’s Healthcare (SVHC) requires speakers, faculty, CME Committee and other individuals who are in a position to control the content of this educational activity to disclose any real or apparent conflict of interest they may have as related to the content of this activity. All identified conflicts of interest are thoroughly evaluated by SVHC for fair balance, scientific objectivity of studies mentioned in the presentation and educational materials used as basis for content, and appropriateness of patient care recommendations.

Joint Sponsorship Accreditation Statement:

This activity has been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education through the joint sponsorship of St. Vincent’s Healthcare and the Duval County Medical Society. St. Vincent’s Healthcare designates this educational activity for a maximum of 1 AMA PRA Category 1 credit.TM Physicians should only claim credit commensurate with the extent of their participation in the activity.

Progress in the management of breast cancer over the last 40 years has resulted in a decrease in breast cancer mortality and morbidity. Major advances include the significant prolongation of life in patients with HER2 positive subset breast cancers and the addition of multiple new agents for the treatment of the most common type of breast cancer, namely the Estrogen Receptor (ER) positive subtype. The identification of the BRCA genes as the main causes of inherited breast cancer, and the identification of drugs that are particularly effective in these subset of patients has also resulted in improved outcomes. Recent findings suggest that checkpoint inhibitors have significant synergism with chemotherapy in the neo-adjuvant setting. Immuno-conjugate drugs for the triple negative breast cancer sub-group are showing significant activity in the refractory setting. The authors predict that the effective personalized combination of these targeted treatments will likely result in the cure of the majority of metastatic breast cancer patients in the next 15 years.

It has been 40 years since the United States Food and Drug Administration (FDA) approved tamoxifen, an oral medication that targets the estrogen receptor which is expressed in over 80 percent of breast cancer cases. Since then, over a million women in the United States (U.S.) in the prime of their lives have succumbed from metastatic breast cancer. Over the past five years, there has been a marked acceleration in drug development against cancer propelled by advancements in basic science, particular molecular biology. A total of eight new targeted drugs against metastatic breast cancer have been FDA approved over the last six years, which is more than the number of drugs approved over the preceding 30 years (Table 1).

Breast cancer is the most common cancer in women in the U.S. with more than 240,000 cases per year and over 40,000 deaths per year.1 Data has shown significant heterogeneity among individual breast cancer cases, particularly in the metastatic setting, which significantly contributes to the almost universal development of treatment resistance and eventual patient’s demise. Despite this, there are multiple reasons to be optimistic, including the fact that new drugs with new mechanisms of action are being developed. It is important to understand the data on recently approved drugs and promising new agents against metastatic breast cancer (Table 2). The data on these agents suggest that the elusive goal of achieving cures for the majority of patients with metastatic breast cancer may be within reach in the next 15 years.

Estrogen Receptor positive disease

The discovery of tamoxifen and the aromatase inhibitors led to a marked improvement in the outcome of patients with metastatic ER positive breast cancer. The m-TOR inhibitor everolimus received FDA approval in 2012 based on the results of the BOLERO2 clinical trial which showed a significant prolongation of progression free survival in the group treated with exemestane and everolimus compared with exemestane as a single agent.2 The last few years have seen the introduction of the cyclin kinase inhibitors (palbociclib, ribociclib and abemaciclib) which nearly doubled the time before progression in the upfront and second line setting treatment for metastatic ER positive breast cancer in combination with anti-estrogen treatments.3,4,5,6 There will likely be development of additional combinations for the treatment of metastatic ER positive breast cancer and the identification of the mutations associated with drug resistance. The discovery of the Estrogen Receptor activation mutations (ESR1 gene mutations in the ligand binding domain) and their associated resistance to aromatase inhibitors will likely lead to the personalized initial treatment of ER positive metastatic breast cancer and the selection of the estrogen receptor degrading inhibitor, fulvestrant or other anti-estrogen agents, over the aromatase inhibitors in this subset of patients.7 The ISPY 2 trial showed marked improvement in pathological complete remission (pCR) with the upfront neoadjuvant addition of pembrolizumab to paclitaxel (an increase in pCR from 19 percent to 39 percent) in ER positive HER2 negative tumors. These results suggest that the early incorporation of pembrolizumab and paclitaxel in the neo-adjuvant (upfront) treatment of patients with locally advanced ER positive breast cancer will likely results in improved outcomes.8 Studies incorporating all of these agents may be feasible given the differences in toxicities associated with these agents. It is likely that these new combinations may result in a greater percentage of patients with metastatic ER positive breast cancer achieving long term control of their disease if not cures.

HER2 amplified breast cancer

Up to one in every four women with breast cancer will harbor tumors with amplification of the HER2 gene. These patients used to have the poorest prognosis among all breast cancer subsets, even worse than that of the triple negative subset, until the introduction of trastuzumab.9 Trastuzumab is a monoclonal antibody that targets the HER2 protein and which was shown to significantly improve survival among patients with HER2-amplified metastatic breast cancer.10 The level of improvement by the addition of trastuzumab to chemotherapy was so significant that it resulted in outcomes that were similar to that of patients with metastatic ER positive HER2 negative tumors, the subset with the best prognosis.9 The subsequent addition of pertuzumab to trastuzumab and chemotherapy in patients with metastatic HER2 positive breast cancer in the Cleopatra trial, led to further significant improvements in overall survival.11 The subset of HER2 amplified breast cancers with increased infiltration of lymphocytes in the tumor had the best response to the combined monoclonal antibodies treatment with up to 40 percent of these patients been free of tumor progression at five years, which represents a remarkable achievement.12 These findings suggest the possibility of significant synergism between combined monoclonal antibodies and checkpoint inhibitors and implies that this combination could potentially lead to a cure for the majority of these patients. The development of the immune-conjugate TDM-1, led to significant improvements in progression free survival and overall survival in the second line setting as compared with the combination of lapatinib and capecitabine.13,14 The development of new, more effective tyrosine kinase inhibitors (neratinib and pyrotinib) is likely to even further improve these outcomes. The newer tyrosine kinase inhibitors are showing significant clinical activity against metastatic disease involving the brain, a common complication in the HER2 positive breast cancers seen in up to 50 percent of these patients.15 The newer immune-conjugate, trastuzumab deruxtecan, has been associated with over 60 percent response rates in patients who failed trastuzumab, pertuzumab and TDM-1.16 These levels of activity are likely to translate into significant improvements in overall survival when these agents are used in the upfront setting. Finally, the checkpoint inhibitor pembrolizumab has shown significant activity with a 15 percent response rate in patients who failed multiple previous systemic treatments including trastuzumab, when added to trastuzumab treatment.17 Given this finding, one could predict significant synergism of pembrolizumab when given in the upfront setting in combination with chemotherapy and dual HER2 inhibition with pertuzumab and trastuzumab. It is quite likely that combination treatments that incorporate the novel tyrosine kinase inhibitors with the newer immuno-conjugates and checkpoint inhibitors will potentially lead to long term control or cure in a significantly higher percentage of patients with metastatic HER2 amplified breast cancer.

Triple negative breast cancer

Tumors that do not express ER and Progesterone Receptor (PR) and do not have amplifications of the ERB2 (HER2) gene (called triple negative breast tumors) have the worst prognosis.9 These tumors are more common in younger patients, in patients with germline BRCA1 mutations, and in African American, Hispanic and Native American subjects.18 Standard of care for these patients consists of systemic chemotherapy, with most patients eventually progressing and dying from their disease. In 2018, olaparib, a Poly (ADP- Ribose) Polymerase (PARP) inhibitor, became the first drug approved for the treatment of metastatic breast cancer in patients with germline BRCA mutations and HER2 negative metastatic breast cancer including triple negative breast cancer, given the findings of greater response rates with less toxicity than single agent chemotherapy.19 Based on the results of the use of these agents in BRCA mutated high grade serous carcinomas of the ovaries, tumors that are genetically similar to triple negative breast cancer, it is likely that the use of these agents as maintenance therapy earlier in the management of metastatic BRCA mutated triple negative breast cancer will likely translate into even greater benefit. Talazoparib is another PARP-inhibitor that will likely be approved for breast cancer in the near future based on the results of the phase 3 EMBRACA trial that showed a significantly higher response rate and duration of treatment response as compared with chemotherapy.20

Immuno-conjugates are another promising new treatment for metastatic triple negative breast cancer. These agents consist of a monoclonal antibody targeting a protein expressed by the triple negative breast cancer cells, attached to a chemotherapeutic agent. Three of these agents are currently undergoing phase 3 clinical trial evaluations and are likely to be approved for clinical use in the near future. Glembatumumab vedotin targets the transmembrane glycoprotein NMB (osteoactivin) which is expressed in over 25 percent of breast cancers. A 30 percent response rate was observed in a phase 2 trial of refractory triple negative breast cancer.21 A phase 3 trial of glembatumumab versus capecitabine is currently underway. Ladiratuzumab vedotin targets the LIV-1 transmembrane protein that is expressed by over 90 percent of breast cancers.22 A 25 percent response rate was observed in 63 patients with metastatic breast cancer who had failed a median of four prior chemotherapies.22 Sacituzumab govitecan is an immuno-conjugate of an anti-TROP-2 antibody linked to SN-38 which is the active metabolite of irinotecan.23 TROP-2 is a surface glycoprotein expressed in over 90 percent of breast cancers. A 34 percent response rate was observed in 110 patients with metastatic breast cancer who had failed two or more previous chemotherapies.

The toxicity profile of PARP inhibitors, checkpoint inhibitors, and the immune-conjugates suggest that combination treatment with these agents may be feasible and could possibly be synergistic. If so, this may translate into significant improvement in overall survival and potential cures.

Over the last six years, new agents have been approved for the treatment of breast cancer than over the preceding 35 years, a result of amazing advancements in molecular biology over the last decade. Currently, at least seven agents with promising preliminary results will likely become FDA approved over the next few years. The expansion of knowledge of the causes of tumor resistance to targeted agents will translate into the development of new agents that could bypass the resistance mechanisms. It is hoped that these developments will translate into cures so that the untimely loss of over 40,000 women in the prime of their lives per year in the U.S. alone can be prevented.

1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2018. CA Cancer J Clin. 2018 Jan;68(1):7-30.

2. Baselga J, Campone M, Piccart M, et al. Everolimus in postmenopausal hormone-receptor–positive advanced breast cancer. N Engl J Med. 2012 Feb 9;366(6):520-9.

3. Finn RS, Crown JP, Lang I, et al. The cyclin-dependent kinase 4/6 inhibitor palbociclib in combination with letrozole versus letrozole alone as first-line treatment of oestrogen receptor-positive, HER2-negative, advanced breast cancer (PALOMA-1/TRIO-18): a randomised phase 2 study. Lancet Oncol. 2015 Jan;16(1):25-35.

4. Turner NC, Ro J, André F, et al. Palbociclib in hormone-receptor–positive advanced breast cancer. N Engl J Med. 2015 Jul 16;373(3):209-19.

5. Finn RS, Martin M, Rugo HS, et al. Palbociclib and letrozole in advanced breast cancer. N Engl J Med. 2016 Nov 17;375(20):1925-36.

6. Sledge GW Jr, Toi M, Neven P, et al. MONARCH 2: Abemaciclib in combination with fulvestrant in women with HR+/HER2− advanced breast cancer who had progressed while receiving endocrine therapy. J Clin Oncol. 2017 Sep 1;35(25):2875-84.

7. Spoerke JM, Gendreau S, Walter K, et al. Heterogeneity and clinical significance of ESR1 mutations in ER-positive metastatic breast cancer patients receiving fulvestrant. Nat Commun. 2016 May 13;7:11579.

8. Nanda R, Liu MC, Yau C, et al. Pembrolizumab plus standard neoadjuvant therapy for high-risk breast cancer (BC): results from I-SPY 2. J Clin Oncol. 2017 May;35(15):506.

9. Dawood S, Broglio K, Buzdar AU, et al. Prognosis of women with metastatic breast cancer by HER2 status and trastuzumab treatment: an institutional-based review. J Clin Oncol. 2010 Jan 1;28(1):92-8.

10. Slamon DJ, Leyland-Jones B, Shak S, et al. Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2. N Engl J Med. 2001 Mar 15;344(11):783-92.

11. Swain SM, Baselga J, Kim SB, et al. Pertuzumab, trastuzumab, and docetaxel in HER2-positive metastatic breast cancer. N Engl J Med. 2015 Feb 19;372(8):724-34.

12. Luen SJ, Salgado R, Fox S, et al. Tumour-infiltrating lymphocytes in advanced HER2-positive breast cancer treated with pertuzumab or placebo in addition to trastuzumab and docetaxel: a retrospective analysis of the CLEOPATRA study. Lancet Oncol. 2017 Jan;18(1):52-62.

13. Verma S, Miles D, Gianni L, et al. Trastuzumab emtansine for HER2-positive advanced breast cancer. N Engl J Med. 2012 Nov 8;367(19):1783-91.

14. Diéras V, Miles D, Verma S, et al. Trastuzumab emtansine versus capecitabine plus lapatinib in patients with previously treated HER2-positive advanced breast cancer (EMILIA): a descriptive analysis of final overall survival results from a randomised, open-label, phase 3 trial. Lancet Oncol. 2017 Jun;18(6):732-42.

15. Freedman RA, Gelman RS, Wefel JS, et al. Translational breast cancer research consortium (TBCRC) 022: a phase II trial of neratinib for patients with human epidermal growth factor receptor 2–positive breast cancer and brain metastases. J Clin Oncol. 2016 Mar 20;34(9):945-52.

16. Doi T, Shitara K, Naito Y, et al. Safety, pharmacokinetics, and antitumour activity of trastuzumab deruxtecan (DS-8201), a HER2-targeting antibody-drug conjugate, in patients with advanced breast and gastric or gastro-oesophageal tumours: a phase 1 dose-escalation study. Lancet Oncol. 2017 Nov;18(11):1512-22.

17. Loi S, Giobbe-Hurder A, Gombos A, et al. Abstract GS2-06: Phase Ib/II study evaluating safety and efficacy of pembrolizumab and trastuzumab in patients with trastuzumab-resistant HER2-positive metastatic breast cancer: results from the PANACEA (IBCSG 45-13/BIG 4-13/KEYNOTE-014) study. Cancer Res. 2018 Feb;78(4 Suppl):GS2-06-GS02-06.

18. Keegan TH, DeRouen MC, Press DJ, et al. Occurrence of breast cancer subtypes in adolescent and young adult women. Breast Cancer Res. 2012 Mar 27;14(2):R55.

19. Robson M, Im SA, Senkus E, et al. Olaparib for metastatic breast cancer in patients with a germline BRCA mutation. N Engl J Med. 2017 Aug 10;377(6):523-33.

20. Litton J, Rugo HS, Ettl J, et al. Abstract GS6-07: EMBRACA: A phase 3 trial comparing talazoparib, an oral PARP inhibitor, to physician's choice of therapy in patients with advanced breast cancer and a germline BRCA mutation. Cancer Res. 2018 Feb;78(4 Suppl):GS6-07-GS6-07.

21. Yardley DA, Weaver R, Melisko ME, et al. EMERGE: A randomized phase II study of the antibody-drug conjugate glembatumumab vedotin in advanced glycoprotein NMB–expressing breast cancer. J Clin Oncol. 2015 May 10;33(14):1609-19.

22. Modi S, Pusztai L, Forero A, et al. Phase 1 study of the antibody-drug conjugate ladiratuzumab vedotin (SGN-LIV1A) in patients with heavily pretreated triple-negative metastatic breast cancer. San Antonio Breast Cancer Symposium; 2017 Dec; San Antonio, TX.

23. Bardia A, Vahdat LT, Diamond J, et al. Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate, as ≥3rd-line therapeutic option for patients with relapsed/refractory metastatic triple-negative breast cancer (mTNBC): efficacy results. San Antonio Breast Cancer Symposium; 2017 Dec; San Antonio, TX.