Israel-based Alpha Tau Medical (Nasdaq: DRTS, DRTSW) reported that intratumoral alpha-emitting radiotherapy combined with pembrolizumab produced objective responses in all nine evaluable patients in a small Phase II study of recurrent or metastatic head and neck squamous cell carcinoma. The findings provide early clinical support for the hypothesis that highly localized alpha radiation may enhance systemic immune checkpoint inhibition, although the results come from an open-label, single-arm trial. Results are being presented at the American Head and Neck Society's 12th International Conference on Head and Neck Cancer.
In the trial, tracked on clinicaltrials.gov, 11 patients received a pembrolizumab lead-in dose followed by intratumoral implantation of Alpha DaRT sources, which were removed roughly two weeks later before patients resumed standard pembrolizumab dosing. Two patients died before response could be assessed—one before receiving Alpha DaRT and one shortly afterward from an unrelated cardiovascular event—leaving nine evaluable patients. Among these, all nine responded systemically by RECIST v1.1 criteria, including four complete responses and five partial responses, for a complete response rate of 44%. Median overall survival reached 18.2 months and median progression-free survival was 5.4 months, with four patients alive at the time of analysis. Alpha Tau said no Alpha DaRT-related serious adverse events occurred, and only two Alpha DaRT-related adverse events were reported, both Grade 1.
The study (NCT05047094) is a single-center, prospective, open-label trial conducted at Hadassah University Medical Center in Jerusalem, designed to enroll up to 48 patients with PD-L1 CPS ≥1 recurrent or metastatic HNSCC using a Simon two-stage adaptive design that allowed early stopping once more than six patients responded; enrollment concluded on that basis after 11 patients were recruited. The results reflect an unblinded, single-arm analysis of a small evaluable cohort of nine patients. Lead investigator Aron Popovtzer said larger controlled studies are needed to confirm the benefit, and Alpha Tau said it is discussing a larger US study with the FDA.