antagonist. 1. a muscle that counteracts the action of another muscle, its agonist. 2. a drug that binds to a cellular receptor for a hormone, neurotransmitter, or another drug blocking the action of that substance without producing any physiological effect itself.
in the body (Figure 20â1). In general, the more widely a cancer spreads, the harder it becomes to eradicate. It is generally metastases that kill the cancer patient. Cancers are traditionally classified according to the tissue and cell type from which they arise. Carcinomas are cancers arising from epithelial cells, and they
Squamous Cell Carcinoma. The second most common cancer of the skin, squamous cell carcinoma is a tumor that occurs in the outer layer of the skin (the epithelium). More than 250,000 new cases of squamous cell carcinomas are diagnosed every year in the United States.