Spider cancer is a term formerly used to describe a cancerous tumor that is edged with thin lines resembling the legs of a spider on X-rays. Their appearance is most likely caused by dilated blood vessels surrounding the tumor.
Telangiectatic cancer is a tumor with many blood vessels attached. In this type of tumor the blood vessels are swollen or dilated and spread out from the tumor. This phenomenon causes a spider-like appearance and was once referred to as spider cancer; however, spider cancer is not a medical term.
Spider cancer is not a type of cancer. Cancerous tumors with a spider-like appearance are not restricted to one type of cancer. This type of tumor can occur in many cancers, such as breast cancer and osteosarcoma. The term is not used in the working medical parlance, but may be used among less medically sophisticated audiences.
Spider cancer is not a type of cancer caused by a spider bite and has no causal relationship to spiders. It is also possible for the term to be used to describe meningioma, a tumor that appears in the arachnoid membrane, which is one of three layers of the membrane that surrounds the brain and spinal cord. The arachnoid membrane has been named after its filmy spider-web-like appearance.