This book aims to examine all immunohistochemical and molecular pathological biomarkers that can be useful and effective in patient diagnosis, prognosis and treatment decision, especially when faced with a carcinoma of unknown primary. For this purpose, epithelial malignancies of all systems and related biomarkers are examined one by one, and to look at the subject through the metastatic regions window, biomarkers that can be used to determine the primary focus for carcinomas seen in the areas most frequently metastasized are emphasized. With this bi-directional perspective, the reader is able to find biomarkers of any type of carcinoma on a system basis, as well as access to which biomarkers can be used when faced with a metastatic carcinoma. The importance of biomarkers in patient follow-up and treatment is also conveyed through the clinician's eye, and so biomarkers are handled with a holistic approach in all aspects. This book primarily targets pathologists, as well as clinicians (oncologists and surgeons) who manage cancer patients.