Ask Mr. Smarty Plants

The University of California Davis Integrated Pest Management (IPM) has an article, Wood Decay Fungi in Landscape Trees, that describes (with photos of the fruiting bodies) several types of fungi that grow in and on trees.  If your tree really does have the Laetiporus sp., the conks (fruiting bodies) showing on the outside of the tree indicate that there is probably extensive internal damage and that the fungus mycelia have been growing inside for many years.  As Michael Kuo says about Laetiporus sulphureus (The Chicken of the Woods):

"The mushrooms do not appear until well after the fungus has attacked the tree; by the time the chickens appear, they are definitely coming home to roost, as far as the tree's health is concerned."

And, from Disease Recommendations for Trees and Shrubs from the University of Michigan Extension Service:

"Fungus invades the roots, trunk and butt of tree through wounds causing a brown cubical rot. First evidence may be the production of a fleshy, yellow shelf fungus on the trunk. However, presence of the fungus suggests considerable rot within and possibility of a hazard tree should be investigated."

It seems that your best bet would be to contact a professional arborist to assess the extent of the internal damage and what the risk is that your tree could fall.   An arborist could also tell you whether there is an effective treatment to save the tree.  To find a professional arborist, you can search on the Tree Care Industry Association (TCIA) site; International Society of Arboriculture (ISA) site and/or the American Society of Consulting Arborists (ASCA).