Tomatoes, normally a staple in many healthy diets, can be made hazardous when canned. The can lining is usually made with a chemical substance called bisphenol-a, more commonly known as BPA.
The FDA is extremely concerned by BPA as it has been shown to alter brain chemistry in research done on rats. As a result, there have been efforts by the Food and Drug Administration to reduce and eventually eliminate BPA from canned food products, not just tomatoes.
The reason canned tomatoes are so so dangerous in particular is because tomatoes are very acidic. Acidic foods can cause more rapid leeching of BPA from the can lining into the food.
The BPA content from canned tomatoes can be so high that some brands warn parents not to feed them to their children.