A First-Time Experience at San Antonio Breast Cancer Symposium

Taylor Monson, PharmD, BCPS, BCOP - Clinical Oncology Pharmacist, The University of Kansas Health System, Kansas City, KS

The 48th annual 2025 San Antonio Breast Cancer Symposium took place December 9-12 in San Antonio, Texas. More than 10,000 breast cancer experts joined in-person and virtually to gain valuable knowledge about new updates in breast oncology care.  This conference included educational and plenary sessions, oral abstracts, and research posters from around the world. While the conference was primarily geared toward physicians and researchers, it emphasized the inclusion of patient advocates and other health care professionals, including pharmacists. 

It was quite exhilarating to be in the room as practice-changing data was presented, and I came home ready to implement new and emerging therapies to shape the care of breast cancer patients better. Additionally, it was an honor to hear the many patient advocates bravely share their stories and experiences as they navigate their journeys with breast cancer.

Below is a summary of some of the practice-changing abstracts presented at this year’s conference.

HER2CLIMB05 - Phase III Trial of Tucatinib with Trastuzumab/Pertuzumab Maintenance in Metastatic Breast Cancer¹

Dr. Erika Hamilton MD, presented results from the HER2CLIMB05 trial, a randomized, phase III trial evaluating the addition of oral tucatinib to IV trastuzumab and pertuzumab for first-line maintenance therapy in the metastatic HER2+ breast cancer. Patients were randomized 1:1 to tucatinib 300 mg orally given twice daily or placebo, given in combination with IV trastuzumab and pertuzumab every 21 days with or without endocrine therapy.

The primary endpoint was investigator-assessed progression free-survival (PFS).  Secondary endpoints included overall survival (OS), PFS per blinded independent central review, central nervous system PFS, and safety. The addition of tucatinib to maintenance trastuzumab and pertuzumab resulted in a median PFS of 24.9 months for the tucatinib arm compared to 16.3 months for the placebo group. Benefit was observed across all subgroups analyzed, including de novo or recurrent disease, hormone receptor status, presence of brain metastases, prior anti-HER2 therapy, best response to induction therapy, visceral or non-visceral disease, ECOG performance status, geographic region, age, and race. This study combination resulted in a 36% reduction in the risk of disease progression or death. The results from this trial were considered both statistically and clinically significant in the first-line setting for HER2+ metastatic breast cancer. The preliminary OS data also trended toward benefit with this combination. The safety profile was manageable and expected, with diarrhea, nausea, and elevated liver enzymes as the most common adverse events. These results demonstrated an enhanced benefit to this regimen in first line maintenance therapy for patients with HER2+ metastatic breast cancer, offering a new potential standard of care regimen. These results were presented in tandem with the publication of the results in the Journal of Clinical Oncology.²

lidERA - Phase III Trial of Giredestrant in Early Breast Cancer³

Dr. Aditya Bardia, MD, MPH, FASCO, presented results from the lidERA trial, a phase III trial evaluating the use of giredestrant vs standard of care (SOC) endocrine therapy (ET) for the adjuvant treatment of patients with estrogen receptor-positive (ER+), HER2-negative early breast cancer. Giredestrant is an oral selective estrogen receptor degrader (SERD). Patients were randomized 1:1 to giredestrant 30 mg orally given daily (in combination with a luteinizing hormone-releasing hormone agonist if appropriate) or SOC ET for 5 years. Patients must have received surgery for their breast cancer within 12 months of the start of study treatment, as well as appropriate neoadjuvant or adjuvant chemotherapy if indicated.

The primary endpoint was invasive disease-free survival (IDFS). Secondary endpoints included OS, distant recurrence-free interval (DRFI), and safety. A total of 4170 patients were randomized. The giredestrant arm demonstrated superior IDFS compared to SOC ET treatment. The 3-year IDFS rates were 92.4% and 89.6%, respectively. A trend toward improvement in OS was noted, but data remains immature at this time. Giredestrant is the first oral SERD to show benefit in early breast cancer. The safety profile was overall well-tolerated and similar to the known adverse-effect profile of this class of therapy. These results are potentially practice-changing and may represent a new standard for patients with hormone-receptor-positive early-stage breast cancer.

DESTINY-Breast05 - Adjuvant Fam-Trastuzumab Deruxtecan for Residual Disease, Interim Update⁴

Dr. Sibylle Loibl, MD, presented an interim update of data highlighting the use of fam-trastuzumab deruxtecan (T-DXd) in the DESTINY-BREAST05 trial. This was a phase III trial comparing the use of fam-trastuzumab deruxtecan to ado-trastuzumab emtansine (T-DM1) in patients with residual invasive HER2+ breast cancer following treatment with neoadjuvant taxane based chemotherapy in combination with anti-HER2 therapy. Patients were randomized to receive either T-DXd 5.4 mg/kg or T-DM1 3.6 mg/kg once every 3 weeks for a total of 14 cycles.

The primary endpoint studied was IDFS. Secondary endpoints were disease-free survival (DFS), OS, DRFI, and safety.  3-year IDFS was 92.3% with T-DXd and 83.5% with T-DM1. This improvement was consistent across all subgroups studied, regardless of the regimen selected for neoadjuvant therapy or HER2 status. In terms of safety, interstitial lung disease occurred in 77 patients (9.6%) treated with T-DXd, with most with grade 1 or 2 events compared with 13 patients (1.6%) in the T-DM1 arm. Additionally, radiation pneumonitis was similar between the arms: 31.4% with T-DXd and 30.5% with TDM-1. The timing of adjuvant radiation therapy did not affect the incidence or severity of ILD in either arm. There was quite a bit of discussion among attendees about the importance of monitoring for both ILD and radiation pneumonitis in this patient population for prompt intervention and management. Overall, T-DXd demonstrated a manageable safety profile, even when given concurrently with radiation therapy in the adjuvant setting. The interim analysis presented helped to highlight further the clinical benefit of T-DXd in the adjuvant setting for HER2+ early breast cancer with residual invasive disease. These results were also published concurrently in the New England Journal of Medicine⁵.

EMBER-3 Trial Updates - Imlunestrant With or Without Abemaciclib

Dr. Komal Jhaveri, MD, FACP, FASCO, presented an update to the EMBER-3 Trial evaluating the use of imlunestrant with or without abemaciclib in advanced breast cancer. EMBER-3 was the first published trial evaluating the use of single-agent imlunestrant, an oral SERD, for HR+ HER2- ESR1-mutated advanced breast cancer. Imlunestrant subsequently received FDA approval for this indication based on improvement in PFS over SOC ET, as previously reported. An additional arm of the trial evaluated imlunestrant given in combination with abemaiclib, and updated efficacy results were presented.

This expanded efficacy update included new PFS results confirming the continued benefit of imlunestrant in this patient population. The median PFS for the imlunestrant plus abemaciclib arm was 10.9 months, compared with 5.5 months for imlunestrant alone, and this benefit was observed across all subgroups analyzed. OS remains immature but there is a trend toward favoring the imlunestrant and abemaciclib combination. The safety profiles for each of these drugs were consistent with previously published data. These updated results were published in tandem with this presentation and highlight the utility of imlunestrant, as a single agent or in combination with abemaciclib, as an option for this subset of metastatic breast cancer patients.⁷ Of note, this regimen is all oral and chemotherapy sparing, which may help guide therapy selection for patients who require or desire an all-oral based treatment regimen.

Overall, the 2025 SABC Symposium was a wealth of new, practice-changing clinical data that will positively shape the future of caring for breast cancer patients. In addition to the updates presented here, the conference emphasized on breast cancer in young women, ctDNA and its use in breast cancer care, and modifiable risk factors to decrease risk including, alcohol use and dietary modifications.

I look forward to the possibility of attending SABCS again in the future and encourage my breast cancer pharmacy colleagues to consider attending as well. The San Antonio Breast Cancer Symposium will be held next year in San Antonio, Texas, on December 8-12, 2026!

References

1.Hamilton E, Curiliano G, Martín M, et al.  HER2CLIMB-05:  A randomized, double-blind, phase 3 study of tucatinib versus placebo in combination with trastuzumab and pertuzumab as maintenance therapy for HER2+ metastatic breast cancer.  Presented at San Antonio Breast Cancer Symposium:  December 10, 2025; San Antonio, TX.  GS1-01.

2.Dieras V, Curigliano G, Martin M, et al. HER2CLIMB-05: a phase 3 study of tucatinib versus placebo in combination with trastuzumab and pertuzumab as first-line maintenance therapy for her2+ metastatic breast cancer. J Clin Oncol. Published online December 10, 2025:10.1200/JCO-25-02600.

3.Bardia A, Schmid P, Martín M, et al.  Giredestrant vs standard-of-care endocrine therapy as adjuvant treatment for patients with estrogen-receptor positive, HER2-negative early breast cancer:  Results from the global Phase III lidERA Breast Cancer Trial.  Presented at San Antonio Breast Cancer Symposium:  December 10, 2025; San Antonio, TX.  GS1-10.

4.Loibl S, Park Y, Sho Z, et al.  Trastuzumab deruxtecan (T-DXd) vs trastuzumab emtansine (T-DM1) in patients with high-risk human epidermal growth factor receptor 2-positive (HER2+) primary breast cancer (BC) with residual invasive disease after neoadjuvant therapy:  interim analysis of DESTINY-Breast05.  Presented at San Antonio Breast Cancer Symposium 2025:  December 10, 2025; San Antonio, TX.  RF6-01.

5.Loibl S, Park YH, Shao Z, et al. Trastuzumab deruxtecan in residual HER2-positive early breast cancer. N Engl J Med. Published online December 10, 2025:NEJMoa2514661.

6.Jhaveri K, Neven P, Lis Casalnuovo M, et al.  Imlunestrant with or without abemaciclib in advanced breast cancer:  updated efficacy results from the phase 3 EMBER-3 Trial.  Presented at San Antonio Breast Cancer Symposium 2025:  December 12, 2025; San Antonio, TX.  GS3-08.

7.Jhaveri KL, Neven P, Casalnuovo ML, et al. Imlunestrant with or without abemaciclib in advanced breast cancer: updated efficacy results from the phase 3 ember-3 trial. Annals of Oncology. Published online December 2025:S0923753425062891. doi:10.1016/j.annonc.2025.11.018