Does solely maintaining a healthy liver prevent the spread of any cancer in the human body? No, that's not true: A Harvard Cancer Center professor of medical oncology told Lead Stories that this claim is "entirely false." Also, the woman making this claim is an unregistered naturopathic practitioner who has been publicly barred from practicing medicine by Australian health officials since 2019.
The claim appeared in an August 5, 2022, YouTube video titled "The Liver - Barbara O'Neill" on the Living Springs Retreat channel. At 1:07 in the video, O'Neill claims that a healthy liver can prevent cancer:
You see cancer cannot get a hold on the body if the liver is working in optimum performance.
This is what the post looked like at the time of writing:
(Source: Screenshot of YouTube.com taken on Wed May 17 18:00:33 2023 UTC)
While the original video was published on YouTube almost a year prior to this writing, a post including it resurfaced in this Facebook reel on May 10, 2023.
The woman speaking in the video is Barbara O'Neill, who, according to this September 24, 2019, public statement (archived here) issued by the Health Care Complaints Commission of New South Wales, Australia, is an "unregistered practitioner" who "makes dubious and dangerous health claims regarding infant nutrition, causes and treatment of cancer, antibiotics and vaccinations that are not evidence based or supported by mainstream medicine."
Timothy Rebbeck, a professor of medical oncology at the Dana-Farber Cancer Institute at Harvard University, told Lead Stories in a May 17, 2023, email that while the liver is crucial to the overall health of the human body, this claim is ultimately false:
I have not heard this claim before and am not quite sure what they mean by a 'healthy liver' (and presumably that there are things that can be done to achieve it), but I cannot think of any reason that a 'healthy liver' would keep cancer from spreading once a tumor exists. The liver certainly plays an important role in detoxifying carcinogens - but I think that's quite different than what is being claimed here.
The claim is entirely false - the liver is important for many other reasons, but this claim has no merit.