Carefully Designing De-escalation Trials in Breast Cancer

Over the past few years, several new, highly effective treatment strategies have improved survival outcomes in patients with early breast cancer.

“We’ve been very fortunate” to see these advances, Sara M. Tolaney, MD, MPH, chief, Division of Breast Oncology, Dana-Farber Cancer Institute, Boston, told attendees at the ESMO Breast Cancer 2024 annual congress.

However, Tolaney noted, these new treatment approaches can come with big limitations — namely, potential overtreatment of some patients as well as short- and long-term toxicities, some of which can be life-threatening.

These caveats have prompted trials exploring strategies to de-escalate therapy, which essentially means providing the right amount of treatment to the right patient at the right time, said Tolaney. The goal is to “right-size” or “optimize therapy” to maintain strong outcomes while mitigating side effects.

De-escalation studies are “critical to preserving quality of life” and affect the cost-effectiveness of therapy, she explained.

But, she added, de-escalation trials are “not a very attractive strategy to pharmaceutical companies” and can be challenging for researchers to conduct. These trials may, for instance, lack adequate sample sizes and sufficient statistical power, which can interfere with achieving clinically meaningful findings that may affect practice.

That is why carefully designing de-escalation trials is crucial, Tolaney said.

In her talk at ESMO Breast, Tolaney highlighted several strategies for designing these trials.

One strategy is to shorten the duration of therapy, said Tolaney.

This approach was explored in the PHARE and PERSEPHONE trials, which looked at 6 vs 12 months of trastuzumab in nonmetastatic breast cancer. Other trials, such as GeparNuevo and KEYNOTE-522, explored whether adjuvant checkpoint inhibitor therapy was needed, or could be skipped, following neoadjuvant therapy. This approach requires establishing noninferiority, or similar efficacy, between the standard of care and the shorter duration of therapy.

A second strategy is to remove part of the chemotherapy regimen, typically the most toxic agent, Tolaney continued.

Conducting a prospective, randomized trial exploring this approach in human epidermal growth factor receptor 2–positive (HER2+) early breast cancer, for example, would be difficult for a range of reasons, such as the need to enroll thousands of patients.

Tolaney and colleagues, however, designed a nonrandomized prospective study — the APT trial — with just over 400 patients to assess adjuvant paclitaxel plus trastuzumab in patients with node-negative HER2+ disease. The open-label, single-arm, phase 2 APT trial found that adjuvant paclitaxel and trastuzumab led to a 10-year recurrence-free interval of 96.3%, 10-year overall survival of 94.3%, and 10-year breast cancer–specific survival of 98.8%.

Outcomes with this adjuvant regimen were comparable to previous findings in historical controls who received doxorubicin, cyclophosphamide, paclitaxel, and trastuzumab or docetaxel, carboplatin, and trastuzumab.

Tolaney concluded that given few events, “it’s unlikely we need to escalate therapy to do better for most patients,” and the APT regimen “can be considered a reasonable and appealing approach for the majority of patients” with node-negative HER2+ breast cancer.

“A single-arm design for a de-escalation study can be practice-changing but only if there are very few recurrences,” Tolaney said.

Substituting chemotherapy with a targeted, potentially less-toxic agent is a third de-escalation approach. The ATEMPT trial compared patients receiving trastuzumab emtansine (T-DM1) with those receiving paclitaxel plus trastuzumab followed by maintenance trastuzumab.

Investigators found that de-escalation with T-DM1 was associated with very few recurrences but similar rates of certain adverse events, including grade 2 or higher neurotoxicity, febrile neutropenia, and grade 4 or higher hematologic toxicity.

However, there are questions about how to define “less toxic,” Tolaney said. The trial found, for instance, that T-DM1 did have some advantages — patients reported better quality of life and experienced less alopecia and neurotoxicity, as well as a less severe impact on fertility.

Understanding the right endpoint to demonstrate less toxicity is critical, “as we start to think about how to replace standard chemotherapies with better targeted drugs,” she added.

The ATEMPT 2.0 trial, which is currently enrolling, will aim to answer some of these questions about defining and demonstrating less toxicity, she said.

Finally, some researchers are attempting to omit chemotherapy altogether with the help of biomarkers. The TAILORx trial, for instance, aimed to stratify patients with early-stage breast cancer by clinical risk factors combined with a 21-gene expression assay and found that adjuvant chemotherapy was not necessary in a large proportion of these women.

On the biomarker front, oncologists might be able to use ctDNA to guide decision-making and personalize therapy, Tolaney said. The presence of ctDNA is associated with an almost 100% likelihood of having a recurrence, whereas its absence suggests better outcomes, she explained.

Oncologists could use the presence or absence of ctDNA to guide next steps — assign patients to follow-up assessments when ctDNA is not present or to standard or experimental treatment when it is present. It may also be possible to leverage the presence of minimal residual disease to help direct treatment choices.

But ctDNA is currently not as perfect a predictor of outcome as it could be, she cautioned. “We need more sensitive assays [so] I’m not sure we’re quite ready to use lack of ctDNA to de-escalate treatment,” she said.

Tolaney declared relationships with Novartis, Pfizer, Merck, Lilly, AstraZeneca, Genentech/Roche, Eisai, Sanofi, Bristol Myers Squib, and other companies.

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