This casebook details key information and findings in PET oncology imaging. PET CT has been increasingly utilized in clinical practice for diagnostic evaluation, initial staging and restaging of malignancies, and plays an important role in optimal patient care. Although F-18 fluorodeoxyglucose (FDG) is still the dominant radioactive tracer in oncology PET imaging services, a handful of new tracers have recently gained the US FDA approval, such as Ga-68 or Cu-64 DOTATATE for carcinoid/neuroendocrine tumors, and F-18 Fluciclovine (AXUMIN) and PSMA for recurrent or metastatic prostate cancers. Clinical interpretation of PET CT oncology scans is often challenging, due to the specific nature of these positron emission radioactive tracers, variable background tracer activities in different organs/tissues with normal variants, complex tumor biology, and wide-ranged treatment responses, especially with emerging and new molecular and immune therapy agents.