Based on significant progression-free survival (PFS) benefits shown in the phase 3 TULIP trial, trastuzumab duocarmazine (SYD985) may provide a new treatment option among HER2-positive metastatic breast cancer patients, according to Cristina Saura, MD, head of the breast cancer program at Vall d’Hebron University Hospital, Barcelona. Dr. Saura presented the results of the TULIP trial (abstract LBA15) on Sept. 19 at the 2021 European Society for Medical Oncology Congress.
Trastuzumab duocarmazine is a novel HER2-targeting antibody-drug conjugate that consists of trastuzumab and a drug containing duocarmycin. Its three-way mechanism of action includes uptake of the antibody-drug conjugate by internalization and intracellular release of duocarmycin with two bystander effects: proteolytic cleavage and subsequent release of payload in the tumor microenvironment and diffusion of active payload to neighboring tumor cells.
While one physician described the results as encouraging, another said the treatment is not nearly ready for primetime.
“It is encouraging to observe clinically meaningful and potentially practice changing progression-free survival improvements in patients receiving treatment in the third line and beyond,” said Aditya Bardia, MD, Massachusetts General Hospital, Boston. “Several agents have been approved as treatments for HER2-positive metastatic breast cancer in recent years including T-DXd, neratinib, tucatinib, and margetuximab. Trastuzumab duocarmazine could eventually be another option.”
Fatima Cardoso, MD, director of the breast cancer unit at the Breast Cancer Research Foundation, New York, said: “At this time there is only a minor 2-month difference in progression-free survival and a nonsignificant overall difference. With the high incidence of ocular toxicity and four toxic deaths, we cannot recommend this drug for clinical practice, in my opinion.”
Two or more prior therapies for metastatic breast cancer
TULIP investigators enrolled 437 patients from 83 sites in 11 countries with HER2-positive locally advanced or metastatic breast cancer who had received two or more therapies for metastatic disease (treatment for brain metastases allowed). They were randomized 2:1 to trastuzumab duocarmazine (1.2 mg/kg every 21 days, 291 patients) or physician’s choice (146 patients) of one of three trastuzumab-containing combinations or lapatinib plus capecitabine. Treatment was continued until progression or unacceptable toxicity. The primary endpoint was centrally assessed PFS.
Longer PFS with trastuzumab duocarmazine
Median age was 57 years, and the median number of prior metastatic breast cancer regimens was 4.7. Centrally reviewed PFS was significantly longer in the trastuzumab duocarmazine group at 7.0 months versus 4.9 months for physicians choice treatment (hazard ratio, 0.64; 95% confidence interval, 0.49-0.84; P = .002). Subgroup analysis, also centrally reviewed, revealed numerical advantage for trastuzumab duocarmazine over physician’s choice across all categories (except for Eastern Cooperative Oncology Group status 2). Analysis of PFS by investigators showed a similar benefit for trastuzumab duocarmazine (6.9 months vs. 4.6 months; HR, 0.60; P < .001).
A first look at median overall survival showed a nonsignificant advantage for trastuzumab duocarmazine (20.4 months vs. 16.3 months (HR, 0.83; 95% CI, 0.62-1.09, P = .153). The overall response rate (partial or complete response) was similar between groups at 27.8% for trastuzumab duocarmazine and 29.5% for physician’s choice with reductions in target lesion measurement at 70.2% and 32.2% for trastuzumab duocarmazine and physician’s choice, respectively. The clinical benefit rates were 38.5% for trastuzumab duocarmazine and 32.2% for physician’s choice.