Cancer is a fungus and citrus is the main contributor.
Cancer is not a fungus. There are fungal triggered cancers like Aspergillus niger induced liver cancer from the aflatoxins produced by the fungus. But fungal induced cancers are pretty rare. The vast majority of cancers are viral in origin.
And cancer cells are not fungi themselves. To begin with cancer cells have cell membranes, while fungi have cell walls. They are not even related to each other.