Oncology is the study of

a. infectious diseases 

b. protozoan parasites

c. tumor

d. cancer

Oncology refers to the branch of science that deals with tumors and cancers. Onco means "bulk," "mass," or " tumor," and "-logy" signifies "study."
There are different types of cancer, but they all begin with the uncontrolled proliferation of abnormal cells. As a result, cancerous cells simply continue to divide, resulting in tumor-like aggregates of cells.