WASHINGTON ― Adding the PD-1 inhibitor pembrolizumab to the established combination of dabrafenib and trametinib (DT) significantly improves survival outcomes in BRAF V600E-mutated anaplastic thyroid cancer ― particularly when administered in a neoadjuvant fashion, prior to surgery. Overall survival rates in the study exceeded 5 years.
"The very long median overall survival in the study's neoadjuvant group is quite remarkable for a group of patients who used to have a very poor prognosis," senior author Maria E. Cabanillas, MD, associate professor in the Department of Endocrine Neoplasia and Hormonal Disorders, the University of Texas MD Anderson Cancer Center, in Houston, Texas, told Medscape Medical News.
"This median overall survival definitely exceeds any other treatments thus far in BRAF-mutated anaplastic thyroid cancer."
The research was presented this week at the American Thyroid Association (ATA) 2023 Meeting.
Anaplastic thyroid cancer, though rare, is the most aggressive form of thyroid cancer. It accounts for just 1% of the cancers but causes about 50% of thyroid cancer mortality.
The historical median overall survival is just 5 to 6 months.
With research in recent years showing that as many as 40% of anaplastic thyroid cancers harbor BRAF V600E mutations, the door has opened for potential benefits with the combination of the BRAF inhibitor dabrafenib with the MEK-inhibitor drug trametinib.
The treatment combination was shown in research that included the phase 2 ROAR trial to yield important responses. It was approved by the US Food and Drug Administration in 2018 for locally advanced or metastatic BRAF V600E-mutant anaplastic thyroid cancer, as well as other cancers.
However, a key caveat of DT is that patients eventually develop resistance mutations, leading to disease progression.
To overcome the problem, Cabanillas and her team found two key strategies that show promise ― the addition of immunotherapy, such as pembrolizumab to DT, and the use of a neoadjuvant approach, with surgery performed after an initial response to the triplet therapy.
Triple Therapy Showed Highly Favorable Results
In a study presented at the 2022 ATA annual meeting, researchers reported on the triple therapy of BRAF/MEK inhibitors vemurafenib and cobimetinib plus immunotherapy with atezolizumab. Results were highly favorable, with an overall response rate of 72% and an impressive 2-year survival of 67%.
However, a major limitation was that the study lacked a control arm. In the current study, the addition of pembrolizumab to DT was compared with DT alone. The investigators also sought to determine the survival benefits of a neoadjuvant strategy.
For the study, first author Sarah Hamidi, MD, also of the MD Anderson Cancer Center, and her colleagues identified 94 patients with BRAF-mutated anaplastic thyroid cancer who were treated either with first‐line DT or DT plus pembrolizumab between 2014 and 2023, either outside of a trial or in a reported clinical trial.
The study compared three treatment regimens ― DT alone (n = 23), DT with pembrolizumab added before or after disease progression (n = 48), and DT with neoadjuvant pembrolizumab added prior to or after surgery (n = 23).
There were no significant differences in baseline characteristics between the groups. Metastatic disease was present at the start of treatment among 87.0% of the DT group, 79.2% of the pembrolizumab group prior to or after disease progression, and 65.2% of the neoadjuvant pembrolizumab group.
The median follow-up of the three groups was 102 months, 28 months, and 42 months, respectively. The median overall survival was 9 months with DT alone, vs 17 months with DT plus pembrolizumab before or after progression and 63 months with neoadjuvant pembrolizumab plus DT (P < .001).
The 12- and 24-month survival rates with DT alone were 33.7% and 28.9%, respectively; for DT plus pembrolizumab before or after progression, the rates were 60.2% and 36.5%; and for neoadjuvant pembrolizumab plus DT, the rates were 80.7% and 74.5%.
In an analysis that did not include the neoadjuvant group, median progression-free survival was significantly longer with DT plus pembrolizumab as an initial treatment (11.0 months) compared with DT alone (4.0 months; P = .049).
A subanalysis that evaluated the timing of the addition of pembrolizumab to DT before or after disease progression showed no significant differences between the two in median overall survival (17 months vs 16 months; P = .554).
"This is valuable information, especially for centers where pembrolizumab cannot be easily obtained as a first-line therapy for anaplastic thyroid cancer," said Hamidi in presenting the findings.
She noted, however, that the results should be interpreted with caution, given the small number of patients who received pembrolizumab before progression (n = 34) and especially after progression (n = 14).
In terms of safety, there were no grade 5 adverse events (AE); 32.4% of patients experienced immune‐related AEs, most frequently, colitis and hepatitis.
Therapies "Improve Survival"
Overall, the results are important, Cabanillas said.
The results are "very exciting when you think about the fact that 10 years ago, patients with anaplastic thyroid cancer had a median overall survival measured in months, and now we see that those with a BRAF mutation have a real chance at survival when managed appropriately from the start," she told Medscape Medical News.
She noted that a key caveat is the study's retrospective nature. Other important considerations are that pembrolizumab adds toxicity as well as cost, and it is largely used off label in anaplastic thyroid cancer.
Nevertheless, "it does feel like there needs to be a call to action in the guidelines for this disease so that it includes neoadjuvant DT or DT plus pembrolizumab as the primary treatment of patients with BRAF-mutated anaplastic thyroid cancer because the initial treatment is critical here," Cabanillas said.
She added that a phase 2 trial with neoadjuvant DT plus pembrolizumab is ongoing. Enrollment is expected to be completed soon.
Commenting on the findings, Sarimar Agosto Salgado, MD, of the Department of Head and Neck–Endocrine Oncology, H. Lee Moffitt Cancer Center and Research Institute, in Tampa, Florida, who was a co-moderator of the session, said the results are encouraging.
"These findings are promising because they open the landscape of options of therapies that we can provide these patients," she told Medscape Medical News.
"Anaplastic thyroid cancer has been a disease with a very short survival despite aggressive therapies, but we are seeing that not only have these therapies been able to improve survival but also patients' quality of life."
Particularly encouraging is how quickly the therapies can work, Salgado added.
"Many times when patients present to the clinic, the rapid response to these systemic therapies can even [allow them to avoid] having a tracheostomy, and we're also seeing that some of these patients are able to go from unresectable disease to resectable disease, and then by having the main tumor out, their survival improves.
"So, this is definitely a big ray of hope for these patients."
Cabanillas has received research funding from Merck. Hamidi has disclosed no relevant financial relationships. Salgado has relationships with Lilly and Exelixis.
American Thyroid Association (ATA) 2023 Meeting.
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Cite this: Triple Therapy Boosts Anaplastic Thyroid Cancer Survival - Medscape - Sep 29, 2023.