Conference Coverage

Ado-trastuzumab highly efficacious for rare HER2-amplified SGCs



– Ado-trastuzumab emtansine, previously known as T-DM1, is highly efficacious in patients with HER2-amplified salivary gland cancers, according to findings from an ongoing phase 2 multi-histology basket trial.

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Dr. Bob T. Li

In fact, nine of 10 patients with this rare tumor responded to treatment with the HER2-targeted antibody drug conjugate after prior trastuzumab, pertuzumab, and anti-androgen therapy, and 5 of those had a complete response, Bob T. Li, MD, said at the annual meeting of the American Society of Clinical Oncology.

“We are reporting this study early because it has already met its primary endpoint,” said Dr. Li of Memorial Sloan Kettering Cancer Center, N.Y.

The 90% response rate was based on either Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 or Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST) criteria; the latter was used because many patients with HER-amplified salivary gland cancer aren’t “RECIST measurable” due to presentation with only lymph node- and bone-only metastasis, he explained, adding that “many of the responses were quite durable, with some lasting 2 years.”

Even at a median of 12 months, neither duration of response nor median progression-free survival have been reached, he said.

Study subjects included nine men and one woman with salivary gland cancers (SGCs) and HER2 amplification identified by next-generation sequencing (NGS). They had a median age of 65 years and a median of 2 prior lines of systemic therapy.

Dr. Li described one patient who had bone and vertebral metastases.

“After just two doses, he had a complete metabolic response,” he said. “His symptoms improved, his pain went away, he feels well, and just recently he celebrated his 92nd birthday.”

Treatment, which included 3.6 mg/kg delivered intravenously every 3 weeks until disease progression or unacceptable toxicity, was well tolerated; toxicities included grade 1 or 2 infusion reactions, thrombocytopenia, and transaminitis. Two dose reductions were required, but no treatment-related deaths occurred, Dr. Li said.

SGCs are rare tumors accounting for only about 0.8% of malignancies. There is no approved therapy for metastatic disease, and due to the rarity of the disease there is no established standard of care, he said, noting, however, that chemotherapy and anti-androgen therapy are considered treatment options based on some retrospective case series.

“Now, coming in from a molecular angle, HER2 amplification turns out to be very common in this rare tumor,” he said.

In fact, NGS of more than 40,000 tumors using the MSK-IMPACT 468-gene oncopanel showed that HER2 amplification occurs in 8% of all SGC histologies, and additional published data show that it occurs in about 30% of those with “the very aggressive salivary duct carcinoma histologic subtype,” he said, adding that case reports and a phase 2 study reported at ASCO 2018 showed encouraging response rates with chemotherapy plus trastuzumab.

Ado-trastuzumab emtansine is a Food and Drug Administration-approved agent for the treatment HER2-positive breast cancer.

“It’s got the trastuzumab antibody, it has a linker which attaches the highly toxic DM1 chemotherapy to it, and ... it binds to the over-expressed HER2 receptor and uses that receptor to internalize the drug into the cancer cell and by lysosome deregulation release the highly toxic DM1 into the cell to cause cancer cell kill,” he explained. “We hypothesized that this drug, as a single agent, would be efficacious in HER2-amplified SGC tumors, and it turns out [that] recently there was a nice case series published from the University of Pennsylvania supporting this hypothesis in a group of patients.”

Indeed, the findings are encouraging and warrant cohort expansion to confirm the results, he said.

Of note, HER2 amplification by NGS (fold change 2.8 to 22.8) correlated with findings on fluorescence in situ hybridization (FISH) in 8 of 8 patients tested, and with immunohistochemistry (IHC) 3+ in 10 of 10 patients tested, thereby confirming the validity of this testing method for the biomarker and as a study entry criterion, he said, adding that ongoing correlative analyses are focusing on cell-free DNA NGS to look for acquired resistance, quantitative HER2 protein analysis by mass spectrometry, and also a dimerization assay looking at the degree of HER2-HER3 dimerization, which leads to receptor internalization that may predict response to HER2 antibody drug conjugates.

“We wanted to see why [HER2-amplified SGC patients] respond so well in contrast to the other diseases in the basket trial,” Dr. Li said, explaining that the trial also includes lung, bladder and urinary tract, endometrial, and colorectal cancer cohorts.

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Dr. Vanita Noronha

“However, to me as an oncologist, the most pressing thing is that with these kind of results and with this kind of response rate and progression-free survival ... there are patients in need of this treatment, so that is certainly the priority–to further accrue patients, complete the trial, publish the data, and hopefully have this new treatment approved to benefit all patients,” he concluded.

Discussant Vanita Noronha, MD, noted that the survival data are immature but “very clinically relevant and clinically significant,” and that they fulfill an unmet need.

“As much as we would like to have randomized trial, this is really a challenge in these kind of rare tumors,” said Dr. Noronha, a professor in the Department of Medical Oncology at Tata Memorial Hospital in Mumbai, India. “So my take-home message ... is that HER2neu is an important molecule driver in salivary gland tumors [and] all patients with salivary gland cancers should be tested for HER2neu amplification.”

Ado trastuzumab emtansine appears to be a good treatment option in those with HER2 amplified SGC, she added.

“Is this a practice changing study? Yes, potentially it is,” she said, noting that in patients with recurrent/metastatic SGC not amenable to radical therapy who are found to have HER2neu amplification, treatment options include either ado trastuzumab emtansine or the combination of trastuzumab and chemotherapy.

Dr. Li reported consulting or advisory roles with Biosceptre International, Guardant Health, Hengrui Therapeutics, Mersana, Roche, and Thermo Fisher Scientific. He reported research funding to his institution from AstraZeneca, BioMed Valley Discoveries, Daiichi Sankyo, GRAIL, Guardant Health, Hengrui Therapeutics, Illumina, and Roche/Genentech. Dr. Noronha has received research funding (to her institution) from Amgen,and Sanofi Aventis.

SOURCE: Li B et al., ASCO 2019: Abstract 6001.

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