Paraneoplastic syndromes in cancer involve excessive production of substances by multiple means. A common substance found in excessive amounts resulting from cancer paraneoplastic syndromes is a. calcium. b. potassium. c. tumor necrosis factor. d. insulin.

The correct answer is option a. "calcium".

Explanation:

A paraneoplastic syndrome is a set of symptoms that a person experience as a consequence of suffering from cancer. The levels of calcium are usually elevated as a result of paraneoplastic syndrome. This is known as paraneoplastic hypercalcemia, and usually disappears once the tumor is successfully treated.