Malignant tumours are named according to the origin of the tissue from which the tumour has developed. Squamous cell carcinoma is an important tumour in the skin and in the airways. Basal cell carcinoma is another common tumour of the skin. What is the origin of the tissue from which the cancerous cells initially developed? Osteosarcoma, chondrosarcoma and fibrosarcoma are tumours that develop in bone. If the tumour is identified with the suffix sarcoma, what tissue did it originate from?

Squamous cell carcinoma and basal cell carcinoma are both skin cancers meaning that they developed from tissue that is in contact with the external environment. You can think of the airways has been in contact with the external environment as well because they are in direct contact with air. The ectoderm is the embryonic tissue from which the skin develops. The prefix ecto- always means external. If your dog has fleas then it has an ectoparasite. The mesoderm is the embryonic tissue from which the internal structures of the body such as the muscles and bone develop. The prefix meso- refers to middle.