Neoplasia

Overview – Neoplasia

Neoplasia refers to the abnormal and uncontrolled growth of cells, forming a mass known as a neoplasm or tumour. While some neoplasms are benign and non-invasive, malignant neoplasms—or cancers—can infiltrate surrounding tissue and metastasise to distant sites. Understanding neoplasia is fundamental in oncology and underpins many concepts in cancer biology, histopathology, and clinical oncology.

Terminology of Cancer

Oncology

• The field of medicine focused on the study and treatment of tumours (neoplasms).
• Derived from the Greek word “oncos,” meaning tumour.

Tumour

• Historically referred to swelling from inflammation.
• Now widely used to describe any growth/neoplasm, benign or malignant.

Neoplasia (Neoplasm)

• “New growth” → An abnormal mass of tissue that:
  • Grows more rapidly than normal tissue.
  • Continues to grow even after the original stimulus is removed.
• Arises from the clonal expansion of a single transformed cell.
• Two main components:
  • Proliferating neoplastic (abnormal) cells.
  • Supportive stroma (connective tissue + blood vessels).
• Causes of transformation:
  • Chemical agents (e.g. carcinogens, free radicals)
  • Physical agents (e.g. ionising radiation, UV light)
  • Biological agents (e.g. viruses, chronic inflammation)

Cancer

• A term used specifically for malignant tumours.
• Hallmarks include:
  • Uncontrolled cell growth
  • Invasion of adjacent tissues
  • Metastasis (spread to distant sites)

Key Concepts in Malignancy

Anaplasia

• Indicates poor differentiation; a hallmark of malignancy.
• Histological features:
  • Pleomorphism: Variable size and shape of cells/nuclei.
  • Abnormal nuclear morphology: Large, hyperchromatic, irregular nuclei; multinucleation.
  • Loss of polarity: Disorganised cell growth.
  • Tumour giant cells: Very large cells with multiple nuclei (not to be confused with Langhans giant cells).

Metastasis

• Secondary neoplasms that are discontinuous from the primary tumour but contain identical cells.
• Only specific tumour subclones possess the gene profile required for metastasis.

Mechanisms of Invasion & Spread

1. Infiltration of extracellular matrix
   • Loss of adhesion
   • Collagenase secretion
   • Breach anatomical boundaries
2. Vascular dissemination (intravasation)
   • Tumour cells enter circulation
   • Adhesion to endothelial cells
3. Extravasation & secondary colonisation
   • Adhere to basement membranes at distant sites
   • Examples:
     • Prostate cancer → bone
     • Lung cancer → brain/adrenals

Pathways of Metastasis

• Direct seeding: Spread into body cavities
• Lymphatic spread: Often leads to lymph node involvement
• Haematogenous spread: Common in liver, lungs, kidneys

Classification & Naming of Neoplasms

Benign Neoplasms

• Naming: [Cell type] + “-oma”
  • Fibroma, Chondroma, Osteoma, Leiomyoma, Rhabdomyoma
  • Adenoma (glandular), Papilloma (wart-like), Polyp (mucosal projection)
• Exceptions (malignant despite “-oma” suffix):
  • Lymphoma, Melanoma, Seminoma, Teratoma (may be benign or malignant)

Histological Features

• Well-differentiated (minimal anaplasia)
• Slow growth rate (months–years)
• Localised, cohesive mass
• Often encapsulated
• Do not metastasise

Malignant Neoplasms

• Naming:
  • “-sarcoma” for mesenchymal/connective tissue (e.g. fibrosarcoma)
  • “-carcinoma” for epithelial tissue (e.g. adenocarcinoma, squamous cell carcinoma)

Histological Features

• Poorly differentiated (highly anaplastic)
• Rapid growth
• Local invasion
• Frequent mitotic figures
• Metastasis is common

Benign vs Malignant Neoplasms – Comparison

Grading & Staging of Tumours

Purpose

• Guides prognosis and treatment decisions
• Enables consistent classification across centres

Grading – Histological Assessment

• Based on degree of anaplasia and mitotic activity
• Grade 1: Well-differentiated, few mitoses
• Grade 2–3: Intermediate
• Grade 4: Poorly differentiated, numerous mitoses

Staging – Extent of Spread

• Based on TNM system:
  • T (Tumour size)
    • T0: In situ
    • T1: <5 cm
    • T2–T4: Larger lesions
  • N (Lymph node involvement)
    • N0: None
    • N1+: Number of nodes involved
  • M (Metastases)
    • M0: None
    • M1+: Distant spread

Example of Combined Grading & Staging

• Grade 1 – T1, N0, M0 → Early-stage, well-differentiated
• Grade 4 – T3, N2, M1 → Aggressive, high-stage malignancy

Summary – Neoplasia

Neoplasia encompasses the abnormal growth of tissues due to loss of regulatory control. While benign neoplasms remain localised and slow-growing, malignant tumours—cancers—exhibit invasion, anaplasia, and metastasis. Understanding the terminology, classification, histological features, and TNM system is critical in assessing prognosis and guiding treatment. For a broader context, see our Genetics & Cancer Overview page.