The cancer-related substances contained in fiddlehead ferns are phenyl oxalic acid, fern lactams, flavonols, aconitin and some substances similar to aconitin. These carcinogens are found in the highest levels in the fern's rhizomes and second highest in the leaves. \x0d\ According to many countries around the world conducting tests on fern cancer, ferns can cause rats to induce intestinal cancer, breast cancer, bladder cancer, leukemia and so on. \x0d\ Scientists have also conducted carcinogenicity tests on cooked and processed fiddlehead ferns showing that even processed fiddlehead ferns can induce cancer. \x0d\ suggests that it is better not to eat ferns.