Citric acid is not carcinogenic. If it would be carcinogenic, all our cells would be transferred to cancer cells, as citric acid is present in all cells near to the DNA (genetic code). Contrary, citric acid is one of the most safe additives that are being used in the food industry. It is completely safe (although not pleasant) to eat 100 gram in a single dose.

If citric acid has anything to do with cancer, is that it has anti-carcinogenic properties...

Why doe some people claim that it is carcinogenic ?

The citric acid cycle is also known as the Krebs cycle, named after it's discoverer Dr. Krebs in the 1930s. Krebs is also the German word for cancer. One group has misinterpreted this in the 1970s as follows :

Krebs cycle = cancer-cycle = citric acid cycle, hence citric acid is very carcinogenic ! This was put on a list of claims of additives published by the (fake) 'Hospital of Paris'. In reality citric acid has nothing to do with cancer.