SAN ANTONIO (FRONTLINE MEDICAL NEWS) – A novel antibody drug conjugate has shown promise in metastatic triple-negative breast cancer (TNBC), according to new findings presented at the San Antonio Breast Cancer Symposium.

Sacituzumab govitecan, a novel antibody-drug conjugate, demonstrated significant clinical activity when used as a single agent among patients with relapsed/refractory disease who had already received multiple lines of therapy. The objective response rate in a cohort of more than 100 patients was 34%, and that included 3 complete responses and 34 partial responses.

“Sacituzumab govitecan demonstrated significant single-agent activity in this population,” said lead author Aditya Bardia, MD , of Harvard Medical School and Massachusetts General Hospital Cancer Center.

“Metastatic triple-negative breast cancer is an aggressive disease with a poor prognosis that tends to affect young women,” said Dr. Bardia. “Visceral and brain metastases are very common. Currently there is no single standard chemotherapy for relapsed or refractory metastatic triple-negative breast cancer.”

He noted that the response rates to standard chemotherapy are low and that median progression-free survival is in the range of 2-3 months. The response rate to standard chemotherapy first line and beyond, based on available data, is in the range of 6-15%.

“Consequently, there is a large unmet need in the breast cancer community,” said Dr. Bardia.

Sacituzumab govitecan (IMMU-132) is an antitrophoblastic cell-surface antigen (anti–Trop-2) and humanized antibody-SN-38 conjugate, which is the active metabolite of the topoisomerase I inhibitor irinotecan. Trop-2 is highly expressed in most epithelial cancers, including TNBC. A phase 1/2 basket trial was previously conducted in a cohort with multiple, advanced epithelial cancers and showed encouraging activity.

Dr. Bardia and his group also published preliminary results earlier this year in patients with metastatic TNBC, which showed an objective response rate of 30%, and last year, sacituzumab govitecan was granted Breakthrough Designation by the Food and Drug Administration. In the current study, the authors expanded the cohort and looked at a more defined population (third-line setting or greater in metastatic TNBC).

In this study, 110 patients who had metastatic TNBC (109 female, 1 male) and had received two or more lines of therapy for metastatic disease were enrolled between July 2013 and February 2017. The cohort included 53 patients from the investigators’ previously reported study in metastatic TNBC (n=69 total). As of this study’s cutoff date (June 30, 2017), 66 patients had died, 30 were in long term follow up, and 14 were still on treatment.

All patients were treated at the 10 mg/kg dose level, receiving 14.5 median doses (range, 1-88) over a median duration of 4.9 months. Treatment was administered on day 1 and 8 in a 21 day cycle, until progression or unacceptable toxicity.

Within the cohort of this heavily pretreated group, 41% received sacituzumab govitecan as third-line therapy while 59% received it at fourth line or more. The majority of patients had previously received taxanes or anthracyclines, and of note, 75% had previously received prior platinum, and 17% had previously received checkpoint inhibitors.

The clinical benefit rate, calculated using the rate of complete and partial response and stable disease greater than 6 months, was 45%. Responses were durable, with a median duration of 7.6 months by local assessment and 9.1 months by central review.

The median progression-free survival was 5.5 months (95% confidence interval, 4.8-6.6) and median overall survival was 12.7 months (95% CI, 10.8-13.6). Of the long term responders, nine have been progression free for more than a year, and four for more than 2 years. At the time of data cutoff, 12 responders were still receiving treatment.

Of note, Dr. Bardia said, patients stayed on sacituzumab govitecan longer than they had stayed on their most recent previous therapy.

The authors also conducted an exploratory subset analysis but found no difference in response when looking at age, prior regimens, onset of metastasis, the presence of visceral involvement at study entry, or Trop-2 expression.

Response among patients who had previously received checkpoint inhibitors was 47%, but Dr. Bardia cautions that “these numbers are small.”

Treatment with sacituzumab govitecan was well tolerated overall, with 2 patients discontinuing the drug because of related toxicity, and no antidrug antibodies detected. Grade 3 or greater toxicity included neutropenia (39%), leukopenia (14%), and anemia (10%); the incidence of febrile neutropenia was low (7%). There was a high rate of gastrointestinal related toxicity, but the majority were grade 1-2, and the rate of grade 3-4 “was in the single digits, ranging from 5-8%,” said Dr. Bardia. There were no drug-related deaths.

Given the high unmet medical need among patients with metastatic TNBC, data from this trial is being sent to the FDA to be considered for accelerated approval, and a global confirmatory randomized Phase 3 is now underway. “The ASCENT trial is recruiting in the United States right now,” said Dr. Bardia; this trial will include patients with metastatic TNBC who will receive either sacituzumab govitecan or physician’s choice of standard therapy.

Additional studies including rational combinations are currently being evaluated for metastatic TNBC and other breast cancer subsets.

SOURCE: Bardia A et al. Abstract GS1-07.


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