They are becoming more and more common. Agrawal et al. (2022) used data from 2002 to 2021 and found that the FDA approved:
…176 new indications for malignant hematology and oncology based on single-arm trials, including 116 accelerated clearances (AA) and 60 traditional clearances. Overall, 87 approvals (49%) were for new molecular compounds or originator biologics, and 89 (51%) were additional indications. Response rate (RR) was the most common endpoint used to support approval in these single-arm studies (173 of 176). [98%]). Of the 116 AAs based on single arm studies, 45 (38%) met their post-marketing requirements for evidence of clinical benefit, 61 (52%) are awaiting evidence of benefit, and 10 (9%) have been withdrawn from the market. as of December. 31st, 2021.