HER2-Low and -Ultralow Populations Benefit from T-DXd in HR+ mBC

Aditya Bardia, MD, MPH, FASCO

Professor, Department of Medicine, Division of Hematology/Oncology

Director of Translational Research Integration

UCLA Health Jonsson Comprehensive Cancer Center

Los Angeles, CA

KEY TAKEAWAYS FROM ADITYA BARDIA, MD, MPH​, FASCO

1. Trastuzumab deruxtecan and sacituzumab govitecan can be given to patients with metastatic HER2-low breast cancer after endocrine therapy and chemotherapy.
2. Progression-free survival and overall survival favor trastuzumab deruxtecan over chemotherapy in HER2-low disease.
3. The DESTINY-Breast06 trial showed similar outcomes for HER2-low and HER2-ultralow disease.

CASE SUMMARY

• A 52-year-old postmenopausal woman underwent breast-conserving surgery plus radiation therapy for pT2 N1 invasive ductal carcinoma of the right breast, grade 2, estrogen receptor (ER)–positive, progesterone receptor–positive, HER2 1+ by immunohistochemistry (IHC); 21-gene recurrence score: 27​.
• She received dose-dense doxorubicin and cyclophosphamide followed by paclitaxel and completed 10 years of tamoxifen.​
• Five years later, she presented with disease recurrence in the liver, hormone receptor–positive, HER2-low, no actionable mutations on tissue next-generation sequencing​.
• She received first-line letrozole plus ribociclib​ (Kisqali).
• ​She went on to receive ​fulvestrant for 6 months to disease progression in the bone and liver, then everolimus plus exemestane for 4 months to disease progression, followed by capecitabine for 6 months until disease progression.
• Repeat circulating tumor DNA next-generation sequencing at each progression showed no actionable alteration.

Targeted Oncology: Do you consider this patient with metastatic breast cancer (mBC) to be eligible for sacituzumab govitecan (Trodelvy)?

Aditya Bardia, MD, MPH​, FASCO: If you look at the label of sacituzumab govitecan, it says 2 prior lines of systemic therapy; it does not say which kind, so you can make a case that the endocrine-based treatment was also systemic therapy.¹ But the TROPiCS-02 trial [NCT03901339], which led to approval, required 2 prior lines of chemotherapy. Purely from a trial perspective, you should give 2 lines of chemotherapy, but in routine clinical practice, after capecitabine, that's when we consider trastuzumab deruxtecan [T-DXd] and sacituzumab govitecan.

Can you use T-DXd and sacituzumab one after another?

You can use them in sequence. There have been studies looking at the efficacy of one after the next,² and there is some cross-resistance between these agents because they have similar payloads. In sacituzumab govitecan, SN38 is a topoisomerase-1 inhibitor. With T-DXd, deruxtecan is also a topoisomerase-1 inhibitor. But in some patients, it does work, and maybe in that setting, the disease progression is more because of the antigen, and so you're using a different antibody that works. But in some patients, you would see cross resistance.

If you look at our guidelines, you have both these drugs, T-DXd and sacituzumab govitecan. The guidelines would suggest T-DXd should be preferred for HER2-low disease.³ But if a patient is not a candidate for T-DXd, that's when you use sacituzumab. That could be either contraindication to T-DXd, or if a patient has HER2 IHC 0 mBC in that setting, you can use sacituzumab, and you can use them in sequence. If you start with one, you can use the other drug after that.

What data support the use of T-DXd in patients with HER2-low status?

This was based on DESTINY-Breast04 [NCT03734029], which looked at T-DXd vs standard chemotherapy for HER2-low, ER-positive breast cancer. It showed impressive improvement in both progression-free survival [PFS] and overall survival [OS]. We saw updated results last year, and essentially continue to see benefit with T-DXd vs a standard chemotherapy with median OS of about 24 months [vs 17.6 months for chemotherapy; HR, 0.69; 95% CI, 0.55-0.87].⁴ That's 2 years in the second line [and beyond] setting.

At least in DESTINY-Breast04, HER2 IHC 1+ vs 2+ didn't matter. We saw similar results, and in DESTINY-Breast04, any prior HER2-low specimen was allowed. That could be primary breast cancer. It could be the first metastatic [biopsy] specimen. Any prior specimen that was HER2-low was allowed, and they saw similar benefit. In terms of safety, the main adverse events [AEs] with T-DXd are neutropenia, alopecia, nausea, and then pneumonitis.

What is the significance of the DESTINYBreast06 trial (NCT04494425) in mBC?

DESTINY-Breast06 also included HER2-ultralow, which is IHC 0+, so just some cells with HER2 expression. The other big difference was it did not require prior chemotherapy for metastatic disease. The comparator was capecitabine, which was 60% in this trial, or taxanes.

It showed results somewhat similar to DESTINY-Breast04, maybe a bit less in terms of HR, but still meaningful [in the HER2-low subgroup]. The HR was 0.62 [95% CI, 0.51-0.74; P < .0002] and a 5-month improvement in PFS [median, 13.2 months vs 8.1 months with chemotherapy].⁵

Then if we combine both HER2-low and -ultralow, in the intent-to-treat population, there were very similar results [PFS HR, 0.63; 95% CI, 0.53-0.75; P < .0001]. In terms of OS, there was a trend towards improvement in OS [HR, 0.83; 95% CI, 0.66-1.05] but the results are not mature at this time.

If we just look at HER2-ultralow, there were very similar results, improvement in PFS with a delta of about 5 months [median, 13.2 months vs 8.3 months for chemotherapy; HR, 0.78; 95% CI, 0.50-1.21], and a trend towards improvement in OS as well [HR, 0.75; 95% CI, 0.43-1.29].

Then if you look at response rate, it was close to 60% overall response rate with T-DXd, even with HER2-ultralow. That’s why we feel that this drug works regardless of the amount of HER2 expression.

In terms of AEs, nausea is the most common, with alopecia, and some diarrhea as well. This is a setting where you should remember to get EKGs, because you can have decrease in left ventricle ejection fraction.

_References:

_{1. Trodelvy. Prescribing information. Gilead Sciences, Inc; 2023. Accessed November 13, 2024. http://tinyurl.com/38uvsw7z}

_{2. Huppert LA, Mahtanai RL, Fisch SC, et al. Multicenter retrospective cohort study of the sequential use of the antibody-drug conjugates (ADCs) trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) in patients with HER2-low metastatic breast cancer (MBC): updated data and subgroup analyses by age, sites of disease, and use of intervening therapies. J Clin Oncol. 2024;42(suppl 16):1083. doi:10.1200/JCO.2024.42.16_suppl.1083}

_{3. NCCN. Clinical Practice Guidelines in Oncology. Breast cancer, version 6.2024. Accessed November 13, 2024. https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf}

_{4. Modi S, Jacot W, Iwata H, et al. 376O - Trastuzumab deruxtecan (T-DXd) versus treatment of physician’s choice (TPC) in patients (pts) with HER2-low unresectable and/or metastatic breast cancer (mBC): Updated survival results of the randomized, phase III DESTINY-Breast04 study. Ann Oncol. 2023;34(suppl 2):S334-S335. doi:10.1016/j.annonc.2023.09.553}

_{5. Curigliano G, Hu X, Dent RA, et al. Trastuzumab deruxtecan (T-DXd) vs physician’s choice of chemotherapy (TPC) in patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 (HER2)-low or HER2-ultralow metastatic breast cancer (mBC) with prior endocrine therapy (ET): primary results from DESTINY-Breast06 (DB-06). J Clin Oncol. 2024;42(suppl 17):LBA1000. doi:10.1200/JCO.2024.42.17_suppl.LBA1000}