Chapter 6: Neoplasia – Cancer Development and Pathophysiology

Malignant cells are characterized by uncontrolled proliferation, a lack of differentiation known as anaplasia, genetic instability, loss of anchorage dependence and contact inhibition, and an infinite life span maintained by high levels of telomerase. The spread of cancer occurs through local invasion, cavity seeding, and distant metastasis, frequently utilizing lymphatic pathways, starting at the sentinel node, or hematologic routes. Successful tumor establishment requires the cancer cells to degrade the extracellular matrix, undergo epithelial-mesenchymal transition (EMT), and promote new blood vessel growth through angiogenesis. The molecular origins of cancer trace back to genetic damage, leading to the transformation of normal proto-oncogenes into activated oncogenes and the inactivation of tumor suppressor genes such as RB and TP53, a process often requiring multiple molecular "hits". This malignant transformation follows a three-stage model of carcinogenesis: initiation, promotion, and progression. Key etiological factors contributing to cancer risk include heredity (e.g., BRCA mutations), immune surveillance failure, exposure to chemical carcinogens, radiation (UV and ionizing), and oncogenic viruses (e.g., HPV and HBV). Clinical manifestations of cancer extend beyond local tissue destruction to systemic issues like the severe metabolic disruption known as cachexia, chronic fatigue, anemia, and paraneoplastic syndromes (symptoms caused by substances secreted by the tumor, often distant from the primary site). Diagnosis relies on various screening tools, the use of tumor markers (e.g., PSA, CEA), histologic grading based on cell differentiation, and clinical staging using the TNM system (Tumor, Node, Metastasis) to assess disease extent. Treatment is multimodal, aimed at cure, control, or palliation, incorporating surgery, radiation, systemic chemotherapy (targeting DNA synthesis or mitosis), hormonal therapy, and modern biotherapy (immunotherapy utilizing agents like monoclonal antibodies and cytokines). Childhood cancers, distinct from adult malignancies, often involve the hematopoietic and nervous systems (e.g., embryonal tumors), and while survival rates are high, treatments frequently lead to serious late effects.