A product may contain & ingredient, known to cause cancer, in lab animals, that does not mean you will get cancer from using the product. It's meant as precautionary warning, & appropriate safety gear can be worn when handling products, with known carcinogens.
This is the only valid reason someone could come up with this claim for 303 product. Someone saw the MSDS sheet, showing a carcinogenic item listed, & wrongly assumed, the product causes cancer. No one in the cancer field has exclusively tested 303 product, to determine, if that particular product causes cancer.
Request from the mfg MSDS sheet, for the product(s) in question, & use in accordance with the safety gear, described.
By doing this you eliminate rumors, fear-mongering, & lies, plus you can use the product safely, avoiding contact with the ingredient in question.
Keep in mind IF this product caused cancer, they would most likely have to file for bankruptcy. Proof does not exist that this product, causes anything, ONLY that it may contain an ingredient that is known to cause cancer, in lab animals. The leap from causes cancer in animals to it causes cancer in humans, is very large, & does not constitute proof. It's a suspect ingredient, where to be safe, precautions should be taken.