Neoplasia - Key Concepts

Neoplasia

• New growth: Abnormal tissue mass exceeding normal tissue growth, continuing post-stimuli.
• Triggered by acquired mutations in a single cell and its progeny.

Classification of Neoplasia

• Based on potential clinical behavior.
• Benign: Proliferate, but don't invade/metastasize.
• Malignant: Invade and/or metastasize; progressive course leading to death without treatment.

Characteristics of benign neoplasia

• Innocent morphology.
• Localized without invasion/metastasis.
• Well-differentiated.
• Good prognosis after surgical removal.
• Slow growth, clearly demarcated.
• Normal nuclear morphology; low mitotic rate; normal mitotic features.
• Clonal chromosome abnormalities, not aneuploid.

Characteristics of malignant neoplasia

• Invasion into adjacent tissues.
• Metastasis to distant sites.
• Variable differentiation range.
• Variable prognosis.
• Rapid growth, not clearly demarcated.
• High mitotic rate, abnormal mitotic features.
• Usually aneuploid.

Fundamental features of benign and malignant neoplasms

• Differentiation and anaplasia.
• Local invasion.
• Metastasis.

Differentiation and Anaplasia

• Differentiation: Neoplasms resemble parenchymal cells of origin.
• Anaplasia: Lack of differentiation; correlates with tumor aggressiveness; reversal of differentiation to primitive level.

Local Invasion

• Benign tumors: Expansile masses localized to origin.
• Malignant tumors: Infiltration, invasion, destruction of surrounding tissues.

Metastasis

• Tumor deposits discontinuous with primary tumor, located in distant tissue.
• Identifies tumor as malignant.
• Increases possibility of death.

Pathways of Spread

• Lymphatic spread: Common for carcinomas; follows lymphatic drainage.
• Hematogenous spread: Usual for sarcomas; cancer cells invade capillaries and venules.
• Seeding of body cavities and surfaces: Tumor metastasis across a body cavity.
• Direct transplantation: By surgical instruments.

Target Organs for Metastasis

• Liver and lungs.
• Brain.
• Bone (vertebral column common).
• Resistant tissues: skeletal muscle and spleen.

Components of Neoplasms

• Parenchyma: Neoplastic cells.
• Stroma: Supporting, non-neoplastic tissue from host (connective tissue, blood vessels, inflammatory cells).

Examples

• Squamous cell: Squamous papilloma (benign), Squamous cell carcinoma (malignant).
• Glandular cell: Adenoma (benign), Adenocarcinoma (malignant).
• Blood vessel: Hemangioma (benign), Angiosarcoma (malignant).
• Cartilage: Chondroma (benign), Chondrosarcoma (malignant).
• Skeletal Muscle: Rhabdomyoma (benign), Rhabdomyosarcoma (malignant).
• Bone: Osteoma (benign), Osteogenic sarcoma (malignant).

Histological Features (Benign vs. Malignant)

• Cellular atypia.
  • Pleomorphism: Variation in cell size/shape.
  • Nuclear abnormalities: Hyperchromatism, clumped chromatin, prominent nucleoli, high nuclear-cytoplasmic ratio, irregular membranes, multiple nuclei.
• Mitotic activity: High count, atypical mitoses.
• Loss of polarity.

Dysplasia

• Abnormal cell organization.
• Loss of uniformity and architectural orientation; considerable pleomorphism.
• Large, hyperchromatic nuclei.
• Mitotic figures more abundant/abnormal.
• Classification: Low- and high-grade dysplasia.

Carcinoma in situ

• Dysplasia of entire epithelial layer without basement membrane invasion.

Carcinomas vs Sarcomas

• Carcinomas: Malignant, from ectoderm/endoderm derived tissue.
  • Examples: Squamous cell carcinoma, adenocarcinoma, hepatocellular carcinoma, renal cell carcinoma.
• Sarcomas: Malignancies, from mesoderm (connective tissues).
  • Examples: Leiomyosarcoma, chondrosarcoma, osteosarcoma, liposarcoma.

Mixed Tumors and Teratomas

• Mixed tumors: More than one cell type, one germ layer.
  • Example: Benign mixed tumor of salivary gland.
• Teratomas: More than one cell type, more than one germ layer; common in ovary.

Neoplasms ending in "-blastoma"

• Resemble primitive embryonic tissues, often pediatric neoplasms.
  • Examples: Retinoblastoma, neuroblastoma, hepatoblastoma, medulloblastoma.

Carcinoma vs. Sarcoma

• Carcinoma:
  • Epithelial origin.
  • More common.
  • Older age.
  • Lymphatic spread.
  • Liver, lung, brain, bone metastasis.
• Sarcoma:
  • Mesenchymal origin.
  • Less common.
  • Any age.
  • Rapid growth.
  • Hematogenous spread.
  • Lung metastasis.