* Cancer is a disease of cellular growth and division. This means it can occur in any organism that has cells that multiply and differentiate.

* Humans are multicellular organisms. While cancer is common in humans, it's not limited to us.

* Unicellular organisms (like bacteria) don't have the same complex cellular structures and mechanisms that can lead to cancer.

* Multicellular organisms (like plants, animals, and fungi) have complex cellular systems that can go awry and lead to uncontrolled growth, which is the hallmark of cancer.

Therefore, cancer can affect a wide range of multicellular organisms, not just humans.