Cancer is serious business. So are alternative cancer treatments — literally, rather than proverbially, in this case.
Dietary Supplements Are Not Held To The Same Standard As Pharmacological Treatments
Pharmacological treatments, or mainstream medications, need to go through a rigorous testing process and can only be sold once they have been proven to be both safe and effective. It makes a certain kind of sense that dietary supplements made using ingredients most of us get through our foods all the time are presumed safe until they're proven to be unsafe, and that the FDA won't complain unless manufacturers venture into the territory of claiming that their products can prevent or cure a particular disease. 
This can become a problem where common household products or foods, or other substances that are generally considered to be safe for human consumption, gather a following among alternative health proponents, however. Though manufacturers do sometimes claim these products can cure cancer, in which case they'd be in violation of the law, they don't even need to in many cases — alternative cancer treatment "groupies" do that job all by themselves. You have people claiming that vitamin C, baking soda, zeolite, aromatherapy, homeopathy, fasting, and an alkaline diet can prevent and even cure cancer.
Apple cider vinegar is one substance that has been claimed to be able to fight cancer. Now, the health benefits of apple cider vinegar are indeed pretty wide-ranging: apple cider vinegar and baking soda help with weight loss, it can help manage your blood glucose levels, probably reduces your cholesterol levels, and is a pretty potent antimicrobial. 
Does apple cider vinegar have any cancer-fighting properties, though, to the point where cancer patients should be using it as an alternative treatment for cancer?
Can Apple Cider Vinegar Be A Natural Cure For Cancer?
You might be surprised to learn that rather a few studies show that vinegar — not apple cider vinegar in particular, but vinegar in general — has the ability to kill cancer cells and reduce the size of tumors. Rice vinegar has been shown to fight colon cancer, bladder cancer, breast cancer, lung cancer, and prostate cancer cells, while sugar cane vinegar kills leukemia cells. [3, 4, 5]
There are, of course, no studies that investigate what happens if someone with cancer foregoes the chance to receive mainstream, evidence-based cancer treatment and replaces it with apple cider vinegar or other kinds of vinegar. That would be unethical, and quite likely to render the study authors murderers.
"Correlation-doesn't-equal-causation" type studies that investigated the link between certain lifestyle choices and an indvidual's cancer risk do exist, however. One Chinese study thus found that eating beans and vegetables, and using plenty of vinegar, was associated with lower odds of cancer . Another study, from Serbia this time, showed that eating liver, canned meat, pork, and using lots of vinegar was actually associated with a higher risk of developing cancer .
Furthermore, research indicates that the consumption of apple cider vinegar protects against oxidative stress — effectively free radicals gone postal due to a lack of antixoidants to combat their harmful effects. This is because vinegar contains polyphenols, which are antioxidants. Polyphenols have indeed been shown to reduce the risk of numerous health conditions, including cancer. 
A review of the health benefits of apple cider vinegar and other vinegars concluded, in light of these findings, that acetic acid may indeed offer some protection against cancer — but also that the available body of scientific evidence on the topic is much too slim to make any definite conclusions. 
The Bottom Line: Apple Cider Vinegar Is Great, But Don't Ditch Your Conventional Cancer Treatment
Apple cider vinegar — and particularly raw, organic apple cider vinegar, or apple cider vinegar with the mother — has attracted a considerable following among people who are interested in alternative health treatments.
Considering that apple cider vinegar has indeed been shown to offer an impressive range of health benefits, it isn't strange if you are considering using an apple cider vinegar drink prior to every meal, as many proponents recommend. While this has certain risks, namely tooth erosion and esophageal injury [10, 11], there is a good chance you can reduce cholesterol and protect your heart health with apple cider vinegar, fight fungal infections, lose weight, and have healthier blood sugar levels.
You may, as research has shown, even reduce your risk of developing cancer.
What if you already have cancer, though? We can only recommend that you strictly follow your oncologist's advice, that you access the full range of recommended mainstream cancer treatments offered to you, and that you discuss the possibility of using a complementary cancer treatment with your treating doctor before you go ahead and try it.