Which of these is NOT a site for metastasis?

The heart is typically not considered a common site for metastasis, which is why it is the correct choice in this context. Metastasis usually occurs in organs that have a rich blood supply and specific biological pathways that support the spread of cancer cells originating from other parts of the body.

Bone, brain, and lungs are well-known sites for metastatic spread because they can create a conducive environment for tumor cells to thrive. For example, breast cancer commonly spreads to bones and the brain, while lung cancer can metastasize to various body parts including bones and the brain as well.

The heart, while it can occasionally be involved in rare cases, does not typically serve as a common metastatic site like the others listed. This is often attributed to the heart's unique anatomic and physiological characteristics, which make it less conducive to the implantation and growth of metastatic tumors compared to other organs.