Studies have shown that flaxseed can reduce tumors in lab animals. So far there's no convincing evidence of a similar action in humans, though some ongoing studies may provide answers. In addition, lignans may play some role in lowering cholesterol and possibly in maintaining bone density. Flaxseed oil usually does not contain lignans, though some processors do add some lignans back into the oil. It is increasingly difficult to single out any one plant food as unique or miraculous.
All plant foods have good things to offer.
So do the herbs we use for flavoring, such as rosemary, thyme, parsley, sage, and so forth. Broccoli and other cruciferous vegetables have anticancer potential. Canola and olive oil and other highly unsaturated oils help lower blood cholesterol. So do oats, which contain the same kind of fiber found in flaxseed. But adding flaxseed to a poor diet is not likely to help much.