Researchers at The University of Texas MD Anderson Cancer Center have reported promising results using a combination of anti-PD-L1 immunotherapy and mutation-directed targeted therapy for treating anaplastic thyroid carcinoma (ATC), a rare and aggressive form of thyroid cancer. The Phase II single-center study, published in JAMA Oncology, demonstrated a significant extension in overall survival (OS) compared to historical outcomes.
The study enrolled 42 patients across three cohorts to assess the efficacy of mutation-matched targeted therapy combined with the immune checkpoint inhibitor atezolizumab. The median OS across all cohorts was 19 months, substantially higher than the historical OS of approximately five months for ATC patients. Notably, patients with BRAFV600E mutations in cohort 1, treated with atezolizumab plus vemurafenib and cobimetinib, achieved a median OS of 43.2 months, marking the longest OS reported to date for systematic therapy in ATC.
Improved Outcomes with Targeted Combinations
According to Maria Cabanillas, M.D., principal investigator and professor of Endocrine Neoplasia & Hormonal Disorders, "Patients with anaplastic thyroid carcinoma need treatments that work fast, and we saw promising results with this combination treatment approach... Based on these findings, we currently use this combination as our standard of care at MD Anderson for patients with ATC and BRAF mutations."
ATC is characterized by rapid progression and poor prognosis, often arising from differentiated thyroid cancer subtypes like papillary and follicular thyroid carcinoma. These subtypes have distinct driver mutations that influence tumor behavior. BRAF mutations, present in about 40% of thyroid cancer patients, have significant therapeutic and prognostic implications.
Cohort-Specific Results
In the trial, 18 patients with BRAF-mutated ATC (cohort 1) received atezolizumab, vemurafenib, and cobimetinib, achieving a 50% objective response rate (ORR) in addition to the median OS of 43.2 months. Cohort 2, comprising 21 patients with RAS (NRAS, KRAS, or HRAS) or NF1/2 mutations, were treated with cobimetinib plus atezolizumab, resulting in a median OS of 8.7 months and a 14% ORR. The three patients in cohort 3, who lacked the aforementioned mutations, received bevacizumab plus atezolizumab, with a median OS of 6.21 months and a 33% ORR.
Overcoming Enrollment Challenges
The trial's success in enrolling 42 patients over four years was notable, given the historical difficulty in recruiting ATC patients for clinical trials. Permissive entry criteria, such as allowing chemotherapy during screening and enabling alternative formulations for oral drug administration via feeding tubes, contributed to this achievement.
Safety Profile
The researchers reported expected side effects based on previous trials involving these drugs. Common adverse events across all cohorts included fatigue, lymphopenia, diarrhea, and anemia. Serious side effects, such as colonic and esophageal perforations, were observed in a few patients.
Future Directions
Cabanillas emphasized the ongoing need for effective therapies for ATC patients with non-BRAF mutations, stating, "There are no approved and effective therapies for ATC with non-BRAF mutations, and we continue to focus our research in that area... We want them to live longer and better lives, and this study offers hope for patients with ATC."
Limitations of the study include the absence of a controlled arm and the acceptance of radiation and surgery, which may have influenced survival outcomes. However, the researchers suggest that future ATC clinical trials should consider allowing surgery due to its potential contribution to improved survival.
