Imagine battling metastatic breast cancer, a disease that has spread beyond the initial tumor site. Now, picture a treatment that not only extends your life but also offers a better quality of life compared to existing options. That's the promise of Trastuzumab Deruxtecan, or T-DXd, a groundbreaking drug that's showing remarkable results, especially for those with HER2-positive metastatic breast cancer. Recent research presented at the prestigious San Antonio Breast Cancer Conference sheds light on just how effective and safe T-DXd can be, even across diverse patient populations.
Two compelling posters presented at the conference (you can explore more at https://www.ajmc.com/conference/sabcs) share a common thread: they delve into the real-world impact of T-DXd on patients with HER2-positive metastatic breast cancer (mBC). This specific type of breast cancer, characterized by an overabundance of the HER2 protein, often requires targeted therapies. The research draws heavily from the DESTINY-Breast clinical trials program, meticulously analyzing long-term safety and effectiveness data from DESTINY-Breast03 (NCT03529110, more details available at https://clinicaltrials.gov/study/NCT03529110) and, crucially, assessing the drug's performance in minority racial and ethnic groups within the US – a population often underrepresented in clinical research.
T-DXd's Long-Term Triumph: A Deep Dive into DESTINY-Breast03
The DESTINY-Breast03 trial was a head-to-head comparison, randomly assigning patients to receive either T-DXd (at a dosage of 5.4-mg/kg, with 261 participants and a median age of 54.3 years) or Trastuzumab Emtansine, also known as T-DM1 (at a dosage of 3.6-mg/kg, with 263 participants and a median age of 54.2 years). Both treatments were administered every three weeks. The results? T-DXd demonstrated statistically significant and clinically meaningful improvements in both progression-free survival (PFS), which measures how long a patient lives without their cancer progressing, and overall survival (OS), a key indicator of how long patients live overall. For this final analysis, the data was reviewed up to June 27, 2025, revealing that significantly more patients in the T-DXd group (24) were still receiving treatment compared to the T-DM1 group (only 2).
Five-year follow-up data painted an even clearer picture. Patients receiving T-DXd were followed for a significantly longer period: 50.9 months (ranging from 0.0 to 80.6 months) compared to 35.4 months (ranging from 0.0 to 80.4 months) for those on T-DM1. The primary reasons for discontinuing treatment were similar in both groups: progressive disease (44.7% for T-DXd vs. a staggering 70.9% for T-DM1) and adverse events (26.8% vs. 10.0%, respectively). But here's where it gets interesting... Fewer patients in the T-DXd group who stopped treatment needed to move on to other systemic anticancer therapies (69.1% vs. 78.4%).
Looking at the bigger picture, the median treatment duration was substantially longer with T-DXd: 18.2 months (ranging from 0.7 to 76.0 months) versus just 6.9 months (ranging from 0.7 to 65.1 months) with T-DM1. Patients on T-DXd experienced a median PFS of 29.0 months (95% CI, 23.7-42.7) compared to a mere 7.8 months (95% CI, 6.8-8.3) with T-DM1. This translates to a remarkable 67% reduction in mortality risk (HR, 0.33; 95% CI, 0.26-0.41). At the five-year mark, PFS was observed in 37.6% (95% CI, 30.8% vs 44.4%) of the T-DXd group, compared to a dismal 10.0% (95% CI, 6.1%-15.0%) in the T-DM1 group. Corresponding overall survival (OS) was 56.4 months (95% CI, 49.4-67.0) and 42.7 months (95% CI, 35.4-52.6), respectively, with 5-year estimated OS rates of 48.1% (95% CI, 41.7%-54.2%) and 36.9% (95% CI, 30.8%-43.1%).
Importantly, there were no fatal treatment-emergent adverse events (TEAEs) in either group. Even more encouraging, exposure-adjusted incidence rates for any-grade, grade 3 or above, and serious TEAEs actually favored T-DXd over T-DM1. This suggests that T-DXd's safety profile is consistent with previous reports, without any new safety concerns emerging, all while confirming its superior effectiveness. And this is the part most people miss... The fact that T-DXd can provide better outcomes with a potentially manageable safety profile is a game-changer for many patients.
Addressing Disparities: T-DXd in Underrepresented Patient Populations
There's an increasing emphasis on ensuring diversity in clinical trials and cancer research. A new investigation focused on minority racial and ethnic groups sheds light on the real-world experiences of patients with HER2+ mBC who received T-DXd as part of the DESTINY-Breast clinical trials. This study specifically looked at patients treated in community oncology settings, reflecting more closely the experiences of patients outside of large academic medical centers.
Researchers analyzed data from the iKnowMed electronic health record, focusing on patients treated with T-DXd (the "index event") between January 1, 2000, and April 30, 2024. The study included patients who had at least one follow-up visit after the start of T-DXd, identified as either Black or Hispanic (the BH group; n = 81; mean age, 56.3 years) or White and non-Hispanic (Wt group; n = 81; mean age, 56.2 years). Patients were followed until death or the final study contact on or before April 30, 2024. The groups were carefully matched for the line of therapy they were receiving (first-line, second-line, etc.) but also adjusted for age. Researchers then used the Kaplan-Meier method to estimate key metrics like time to treatment discontinuation (TTD), time to next treatment (TTNT), and real-world PFS (rwPFS) from the start date of T-DXd.
Interestingly, the BH group had some differences compared to the Wt group. More patients in the BH group had metastasis only in their internal organs (visceral-only metastasis, 65.4% vs. 58.0%), were hormone receptor-negative (27.2% vs. 22.2%), and received T-DXd as a third-line or later treatment (49.4% vs. 43.2%). They also had a slightly lower real-world objective response rate (63.0% vs. 67.9%) and a longer follow-up period (15.2 vs. 13.6 months) compared to the Wt group. Despite these differences, the BH group surprisingly showed better outcomes on two key measures of disease progression:
- rwPFS: 16.6 months (95% CI, 9.9-21.4) vs. 14.7 months (95% CI, 9.8-17.4)
- TTD: 12.5 months (95% CI, 9.7-14.9) vs. 12.2 months (95% CI, 9.7-16.8)
- TTNT: 18.3 months (95% CI, 13.1-22.9) vs. 18.4 months (95% CI, 13.2-21.1)
In terms of side effects, the BH group experienced lower rates of treatment-induced nausea, fatigue, vomiting, diarrhea, and hair loss (alopecia). But here's where it gets controversial... They did, however, have higher rates of neutropenia (low white blood cell count) and interstitial lung disease/pneumonitis (inflammation of the lungs). Also, fewer patients in the BH group chose to start additional treatment after their initial T-DXd treatment. Of those who did, T-DXd-based and T-DM1-based regimens were the most frequently used.
The Bigger Picture: What Does This Mean for You?
These findings from the San Antonio Breast Cancer Conference offer a powerful message of hope for patients with HER2-positive metastatic breast cancer. T-DXd is proving to be a highly effective treatment, offering significant improvements in survival and quality of life compared to existing options. The data also suggests that T-DXd can be effective across diverse patient populations, although further research is always needed to understand the nuances of treatment response in different groups.
One key takeaway is the importance of diversity in clinical trials. While this study provides valuable insights into the use of T-DXd in minority populations, continued efforts are needed to ensure that clinical trials accurately reflect the diversity of the patient population. This will help to ensure that all patients have access to the best possible treatments and that treatment decisions are informed by data that is relevant to their specific circumstances.
What are your thoughts on these findings? Do you believe that T-DXd represents a significant advancement in the treatment of HER2-positive metastatic breast cancer? What steps can be taken to ensure greater diversity in clinical trials and access to innovative treatments for all patients? Share your comments and perspectives below!
References:
- Im SA, Cortes J, Kim SB, et al. Trastuzumab deruxtecan (T-DXd) versus trastuzumab emtansine (T‑DM1) in patients (pts) with human epidermal growth factor receptor 2-positive (HER2+) metastatic breast cancer (mBC): final analysis from DESTINY-Breast03. Presented at: San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, Texas. Poster PS5-01-30.
- Mehta S, Stevens L, Shah R, et al. Real-world effectiveness of trastuzumab deruxtecan in HER2+ metastatic breast cancer by racial and ethnic group – data from US community practices. Presented at: San Antonio Breast Cancer Symposium; December 9-12, 2025; San Antonio, Texas. Poster PS5-01-15.
- Shaw M. DESTINY-Breast data add to accolades for trastuzumab deruxtecan. AJMC®. December 7, 2022. Accessed December 9, 2025. https://www.ajmc.com/view/destiny-breast-data-add-to-accolades-for-trastuzumab-deruxtecan
- Caffrey M. Louisiana delivers innovative cancer treatments, but ensuring access is a work in progress. AJMC. November 25, 2025. Accessed December 9, 2025. https://www.ajmc.com/view/louisiana-delivers-innovative-cancer-treatments-but-ensuring-access-is-a-work-in-progress
- Shaw M, Mewawalla P. Redesigning trials for real-world patient complexity: a Q&A with Prerna Mewawalla, MD. AJMC. December 4, 2025. Accessed December 9, 2025. https://www.ajmc.com/view/redesigning-trials-for-real-world-patient-complexity-a-q-a-with-prerna-mewawalla-md
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