This study of cell cultures (in vitro) was published in June 2021 in the journal Archives of Oral Biology. It used both popular forms of THC, and both showed promising results for oral cancer cell inhibition and apoptosis (cell suicide). Given that oral cancer cells are in the mouth and can be accessed more easily than cancer cells inside the human body, an in vitro study is probably more relevant than most.
"Both cannabinoids were found to decrease cell viability/proliferation" & "Δ9-THC and Δ8-THC also suppressed the migration/invasion"
"We demonstrated that cannabinoids (Δ9-THC and Δ8-THC) were able to decrease oral cancer cell growth through various mechanisms, including apoptosis, autophagy, and oxidative stress. These results suggest a potential use of these molecules as a therapy against oral cancer."
A link to the abstract on PubMed.gov is here, but the paper is behind a pay wall as of today.