Solid tumors contain abnormal and heterotypic cells that communicate through tight and gap junctions. In contrast with liquid tumors, as the cells multiply, they form a “mass” called a solid tumor and usually do not contain pockets of fluid, pus, air, or other substances.

Solid tumors can be either non-cancerous (benign), pre-malignant (cells that have the potential to become malignant), or malignant (cancerous).

Solid tumors represent approximatively 90% of adult human cancers. They can develop in many parts of the human body.