Conference Coverage

Treatment shows 'important improvements' in triple-negative breast cancer



Approximately one-third of the patients treated in the ASCENT clinical trial comparing the antibody-drug conjugate sacituzumab govitecan (Trodelvy, Gilead) with single-agent chemotherapy in patients with triple-negative breast cancer (TNBC) did not have an initial diagnosis of TNBC.

But as a subanalysis of data from the randomized, phase 3 study showed, sacituzumab govitecan was associated with significantly better progression-free survival (PFS) and overall survival among patients without an initial TNBC diagnosis, with efficacy similar to that seen in the overall study population and in patients without known brain metastases, reported Joyce O’Shaughnessy, MD, at the 2021 European Society for Medical Oncology Congress. In her presentation (abstract 258P), Dr. O’Shaughnessy, who is an oncologist with the Texas Oncology–Baylor Charles A. Sammons Cancer Center in Dallas, said that it’s not uncommon to see acquired triple-negative breast cancer in patients who have hormone receptor–positive disease initially and then later on, develop triple-negative breast cancer.

“That is why at the time of metastatic diagnosis we always say that patients should have repeat receptor [testing], because it’s been well described that a subset of hormone receptor–positive breast can become triple negative under pressure from endocrine therapy,” said ASCENT coinvestigator Aditya Bardia, MD, MPH, Massachusetts General Hospital, Boston, in an interview

Coinvestigator Kevine Punie, MD, from University Hospitals Leuven (Belgium), said that “triple-negative breast cancer is a diagnosis of exclusion. This is a heterogenous disease where several biological subsets are merged.”

“It was important to perform this subgroup analysis to reassure us that the treatment effect we see from [sacituzumab govitecan] in the overall population is also observed in this specific subgroup of patients where biologically we’re treating a different disease,” he said in an interview.

Antibody-drug conjugate

Sacituzumab govitecan consists of an antibody targeted to the trophoblast antigen 2 cell surface receptor found on most breast cancer cells, plus the topoisomerase-1 inhibitor SN-38 as its toxic payload.

In the primary intent-to-treat (ITT) analysis of ASCENT, sacituzumab significantly prolonged PFS with a median of 4.8 versus 1.7 months for patients treated with the physician’s choice of either capecitabine, eribulin, vinorelbine, or gemcitabine. The difference translated into an HR for progression with the antibody-drug conjugate of 0.41 (P < .00001).

The subgroup analysis looked at outcomes for 70 patients randomized to sacituzumab govitecan and 78 randomized to single-agent chemotherapy who did not have an initial diagnosis of TNBC.

In all, 27% of patients in this subgroup in the sacituzumab arm and 29% in the chemotherapy arm had received a prior line of treatment with a CDK4/6 inhibitor.

At the time of data cutoff in March 2020, four patients (6%) in the sacituzumab arm remained on treatment versus no patient in the chemotherapy arm. The most common reason for treatment discontinuation was disease progression, which occurred in 84% and 72% of patients, respectively.

The median treatment duration was 5.1 months in the sacituzumab and 1.2 months in the chemotherapy arm. The median duration of follow-up was 10.6 and 6.1 months, respectively.

Progression-free survival, overall survival results

For all patients without an initial TNBC diagnosis, the median PFS was 4.6 months with sacituzumab versus 2.3 months with chemotherapy, which translated into a hazard ratio for progression of 0.48 (95% confidence interval, 0.32-0.72). The progression-free benefit with the antibody-drug conjugate was similar to that seen in the intent-to-treat population, as noted before, and among the overall population of patients in the study with no known brain metastases (HR, 5.6 vs. 1.7, respectively; P < .001).

The objective response rates were 21% in the sacituzumab and 5% in the chemotherapy arm. Objective responses were not affected by the prior use of CDK 4/6 inhibitors.

Median overall survival in this subgroup was 12.4 months with the antibody-drug conjugate versus 6.7 months with chemotherapy (95% CI, 0.30-0.64).

The investigators reported that the safety profile was manageable in this subgroup of patients, with a low rate of treatment discontinuations because of adverse events (5%) and no treatment-related deaths with sacituzumab govitecan.

Health-related quality of life

In a separate poster (abstract 257P) presented at the meeting, the ASCENT investigators reported health-related quality of life results in the overall population.

The mean European Organization for the Research and Treatment of Cancer quality of life questionnaire subscale scores at baseline were similar between treatment arms.

For the major domains of global health status, physical and emotional functioning as well as lower symptomatic impact of fatigue, pain, dyspnea, and insomnia, sacituzumab govitecan showed “significantly and meaningfully greater improvement” than the physician’s choice of chemotherapy, the investigators found.

Of individual symptoms, only diarrhea was worse with the antibody-drug conjugate.

“These were important improvements,” Dr. Punie said, “because we saw improvements in the primary health-related quality of life domains such as global health status. We also saw that the time to clinically meaningful deterioration of quality of life domains were significantly longer for patients treated with [sacituzumab govitecan].”

“Patients who received sacituzumab govitecan had better health-related quality of life as compared to the control arm, and that’s a very important result, because in the metastatic setting our goal is twofold: We want to prolong survival, and we want patients to have improved quality of life,” Dr. Bardia said.

The Ascent trial is sponsored by Gilead Sciences. Dr. Punie disclosed relationships with multiple companies/organizations, not including Gilead. Dr. Bardia disclosed contracted research for Gilead and others, as well as other relationships.

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