Incidence of Carcinomas
During embryogenesis, the three germ layers (endoderm, ectoderm, mesoderm) differentiate into epithelial and non-epithelial cells, which eventually form differentiated tissues and organs . Epithelial cells arise from stem cells and often line body surfaces that interact directly with the environment. The type of epithelium reflects location and function. Epithelial cells are typically attached to underlying connective tissue by a basement membrane, and the underlying stroma includes blood vessels, lymphatic vessels, hematopoietic cells, stromal fibroblasts, extracellular matrix, neuronal structures, smooth muscle and adipose tissue. Neoplasia is the term given to the new growth of cells proliferating without regard to stop signals, with attendant new blood vessels, forming a tumor mass (neoplasm). If the growing neoplasm within an epithelial layer stays restricted by a basement membrane and does not invade that barrier, it is designated as a benign tumor. However, once tumor cells undergo multiple genetic changes and breach and infiltrate through the basement membrane, the neoplasm becomes invasive and malignant, and the cells use proteases and glycosidases, which allow breakdown of the extracellular matrix, reaching and invading blood vessels. Abundant data now indicates that we humans are very closely related to other hominids including chimpanzees, bonobos, gorillas, and orangutans (the so-called "great apes", hereafter called non-human hominids, or NHHs. There has been a considerable body of published information regarding their disease profiles, particularly from primate facilities in the USA. Surprisingly, surveys of this existing information suggest that several common human diseases may be partially or completely unique to our species, and that captive chimpanzee population may suffer from different profiles of pathology. Among these apparent differences in disease incidence, one that has been emphasized in multiple reports is the rarity of occurrence of common human carcinomas in captive chimpanzees.We conclude that while relative carcinoma risk is a likely difference between humans and chimpanzees (and possibly other “great apes”), a more systematic survey of available data is required for validation of this claim.