Background: New treatments are warranted due to limited systemic treatment options for SGC patients (pts). Gallium [68Ga]Ga prostate-specific membrane antigen (PSMA) PET imaging results in SGC pts have demonstrated PSMA expression of SGC and thus indicated that PSMA radionuclide therapy may be a useful option, especially in the case of adenoid cystic carcinoma (AdCC) and salivary duct carcinoma (SDC) subtypes. Therefore, this study (EudraCT number 2019-003857-27) evaluated the safety and efficacy of PSMA-targeted radionuclide therapy in AdCC and SDC pts. Methods: This was a single-center, single-arm, phase II pilot study. R/M AdCC (n = 10) and SDC (n = 5) pts with sufficient PSMA tracer uptake on [⁶⁸Ga]Ga-PSMA PET imaging, i.e., ≥1 lesion ≥1.5cm with PSMA expression above mean liver level, were treated with 2-4 cycles of 7.4 GBq [¹⁷⁷Lu]Lu-PSMA-I&T, with an interval of 6±1 weeks. Baseline imaging was repeated for evaluation 4 weeks after cycle 2; in case of progressive disease (PD) per RECIST 1.1 the treatment was discontinued; otherwise, pts received the full treatment (4 cycles). All pts received whole body post-therapeutic imaging after 1, 24, 48, 72 h and 7d after each cycle. The primary endpoint was safety. Secondary endpoints include the objective response rate, progression-free survival (PFS), and overall survival (OS). Results: Between 6-2020 and 2-2023, 15 AdCC pts and 10 SDC pts were screened for eligibility. Five AdCC pts and 8 SDC pts were screen failures due to insufficient PSMA expression in 11 pts (AdCC n = 4; SDC n = 7) or due to brain metastases in 2 pts (AdCC n = 1; SDC n = 1). Ten AdCC and 2 SDC pts received at least one cycle of 7.4 GBq [¹⁷⁷Lu]Lu-PSMA-I&T. The most observed adverse events (grade 1-2) included: nausea (75%), dry mouth (75%), fatigue (67%), and anemia (58%). Two pts (17%) developed grade 3 toxicity; lymphocytopenia (n = 1) and hyponatremia (n = 1). No grade 4-5 toxicities were observed. Two pts (AdCC n = 1; SDC n = 1) received only 1 treatment cycle due to early PD. The interim-treatment evaluation resulted in the discontinuation of treatment after 2 cycles in an additional 3 AdCC and the second SDC pts due to PD. Six AdCC pts received the full treatment (4 cycles); no responses were observed; 3 pts (75%) showed stable disease of more than 3 months after treatment completion (5, 15 and 21 months); 3 pts showed PD at 3 months after treatment completion. Median PFS in 10 AdCC pts was 6.7 months (95%CI: 0.0-15.1); OS was not reached after a median follow-up of 11.9 months. Conclusions: [¹⁷⁷Lu]Lu-PSMA-I&T treatment in SGC pts is well-tolerated. The efficacy in AdCC was limited; only stable disease was achieved in 3 out of 10 pts. In most screened SDC pts, PSMA expression was insufficient to undergo [¹⁷⁷Lu]Lu-PSMA-I&T treatment; the 2 SDC pts included showed early PD. Dosimetry analyses will be performed to calculate the delivered radiation doses to organs at risk as well as tumor lesions. Clinical trial information: EUCTR2019-003857-27.