Neoplasia: Benign vs Malignant Tumors

Neoplasia

• Neoplasia is an abnormal mass of tissue whose growth exceeds normal tissue growth and persists even after the stimulus that triggered the change has ceased.
• Genetic changes allow for excessive and uncontrolled proliferation independent of normal growth regulatory stimuli.
• Neoplasms are categorized as benign or malignant.

Benign Tumors

• Usually encapsulated by fibrous tissue.
• Grow slowly.
• Grow locally on the surface of affected tissue but don't invade adjacent tissues.
• Do not metastasize (spread to other areas).
• Cells are well differentiated parenchymal cells resembling their original tissue type.
• Often amenable to surgical removal.

Malignant Tumors

• Lack encapsulation.
• Grow rapidly.
• Grow by invasion, destroying and penetrating surrounding tissue.
• Can metastasize (spread to other parts of the body).
• Cells are poorly differentiated, or anaplastic, with significant variation in size and shape.
• May require chemotherapy or radiotherapy after surgical removal.

Components of Benign and Malignant Tumors

• Parenchyma: Transformed cells that give the tumor its specific properties.
• Stroma: Supportive tissue (connective tissue, blood vessels, inflammatory cells) that is important for tumor growth.

Nomenclature

• Benign tumor names typically end in "-oma" (e.g., fibroma, chondroma).
• Benign epithelial tumors are often categorized by macroscopic/microscopic patterns or cell origin.
• Examples of benign epithelial tumors include adenomas, papillomas, polyps, and cystadenomas.

Mixed Tumors

• Can arise from cells undergoing divergent differentiation.
• Salivary gland tumors are an example, which can include both epithelial and mesenchymal components.
• Pleomorphic adenoma is a common example of a mixed salivary gland tumor.

Malignant Tumors: Classification

• Sarcomas: Originate from mesenchymal tissues (e.g., bone, cartilage, fat).
• Carcinomas: Originate from epithelial tissues (e.g., adenocarcinomas - glandular, squamous cell carcinomas - squamous cells, cholangiocarcinomas - bile ducts).

Exceptions

• Teratomas: Develop from totipotent stem cells and contain various tissues (bone, muscle, nerve).
• Lymphomas: Malignant tumors of lymphoid tissues.
• Mesotheliomas: Tumors of the serous membranes.
• Melanomas: Benign tumors are melanocytes, malignant tumors are also melanocytes.

Special Terms

• Hamartomas: Malformations of disorganized tissue native to a specific location (e.g., lung).
• Choristomas: Heterotopic rests of cells (e.g., pancreatic tissue growing outside the pancreas).

Characteristics of Benign and Malignant Tumors

• Differentiation and anaplasia: The extent of similarity between tumour cells and normal cells; well-differentiated tumors resemble normal cells, anaplastic tumors differ greatly.
• Rate of growth: Benign tumors grow more slowly.
• Local invasion: Benign tumors tend to remain localized.
• Metastasis: Malignant tumors can metastasize, spreading to other sites through blood or lymphatic systems.

Differentiation and Anaplasia

• Only applies to parenchymal cells.
• Differentiation refers to the extent to which tumour cells resemble their normal counterparts.
• In benign tumors, cells are usually well differentiated (i.e., resemble normal cells in structure and function).
• Malignant tumors can vary widely, from well-differentiated to anaplastic (undifferentiated).

Anaplastic Features

• Pleomorphism: Significant variation in size and shape of cells.
• Hyperchromasia: Nuclei are dark-staining (more densely packed with chromatin).
• Increased nuclear-to-cytoplasmic ratio: Nuclei are disproportionately large compared to the cytoplasm.
• Coarse chromatin: Clumps of chromatin rather than a dispersed/uniform distribution.
• Large nucleoli: Large structures within the nucleus that create RNA/protein synthesis and replication.
• Numerous and atypical mitoses: Increased number of cell divisions, often with abnormal figures.

Squamous Cell Carcinoma

• Originates from squamous cells and can be well- or poorly differentiated.
• Can exhibit features of anaplasia (variation in size, shape of cells, etc.).

Rhabdomyosarcoma

• Arises from skeletal muscle.
• Undifferentiated cells with numerous atypical/abnormal mitotic figures.

Tripolar Mitosis

• An uncommon type of abnormal mitosis.
• Abnormal mitotic figures appearing three- or four-spindle-shaped.

Dysplasia

• Loss of cell uniformity/morphological/functional features of normal cells.
• Increased mitotic figures may indicate malignancy (rapid cell division).
• Epithelial tissue may revert to normal after the cause of dysplasia is removed in reversible cases.

Rate of Growth

• Some benign tumors may initially grow rapidly then regress.
• Rate of malignant tumor growth tends to correlate with differentiation level-rapidly growing tumors tend to be poorly differentiated.
• Rapidly growing malignant tumors may show regions of ischemia/necrosis.

Cancer Stem Cells and Lineages

• Tumors may have stem cells analogous to normal tissues providing and supporting tumor growth.

Local Invasion

• Benign tumors tend to remain localized at initial site of origin.
• Cancer cells can invade surrounding tissues by progressively infiltrating, destroying, and penetrating them.

Metastasis

• Cancers spread to distant sites through blood or lymphatic systems.
• The liver and lungs (example) are common sites for secondary/metastasis tumors.

Epidemiology

• Cancer incidence depends on environmental conditions, age, and genetic factors.
• Age and accumulation of somatic mutations.
• Environmental factors, presence of cancer in higher rates than in other areas.
• Hereditary cancer syndromes: mutations/gene increases cancer risk (ex. Childhood retinoblastoma).
• Familial cancers: cancers can occur in families in familial forms.