Chapter 9: Principles of Neoplasia

Principles of Neoplasia review explores the fundamental principles of neoplasia, defining the uncontrolled, monoclonal growth of abnormal tissue and establishing cancer as a leading cause of mortality dominated clinically by lung, prostate, breast, and colorectal malignancies. The discussion breaks down the multistep nature of carcinogenesis, differentiating between initiation (mutation) and promotion (proliferation), while categorizing key carcinogenic agents including chemical mutagens like nitrosamines and asbestos, radiation sources such as UVB light which forms pyrimidine dimers, and oncogenic viruses including HPV, EBV, and Hepatitis B. A major portion of the summary focuses on the molecular genetics of cancer, detailing the activation of proto-oncogenes into growth-promoting oncogenes like ERBB2, RAS, and MYC, alongside the critical inactivation of tumor suppressor genes such as p53 and Rb, often explained via Knudson's two-hit hypothesis. The role of apoptosis regulation is examined, specifically how Bcl-2 overexpression prevents cell death in follicular lymphomas via the t(14;18) translocation. The text further contrasts the gross and microscopic features of benign versus malignant neoplasms, highlighting criteria such as encapsulation, differentiation, anaplasia, and mitotic activity. Diagnostic modalities are explored, including the use of immunohistochemistry to detect intermediate filaments like keratin and vimentin, and the clinical utility of serum tumor markers like PSA, CEA, and AFP for screening and monitoring. Finally, the distinction between tumor grading (histologic differentiation) and staging (the TNM system for anatomic spread) is clarified, concluding with an overview of metastatic pathways which notes that while carcinomas typically spread via lymphatics, sarcomas and specific carcinomas like renal cell and hepatocellular prefer hematogenous routes.