Cancer

Content

Cancer

• Classification

• Spread of cancer

Objectives

At the end of this lecture, student will be able to

• Define the term “Tumor”

• List main characteristics of benign and malignant cancer

• Describe the nomenclature used for various types of tumors

• Explain the mechanism of spread of tumors

CANCER

General biology of cancer

Neoplasm/ Tumour - “A mass of tissue formed as a result of abnormal, excessive, uncoordinated, autonomous and purposeless proliferation of cells”

• Oncology– Branch of science dealing with the study of neoplasm

• Transformation from a living normal cell into a living tumor cell

Basic features of change in neoplasia

• Change is irreversible; becomes fixed character of a transformed cell

• Acquired fixed character is heritable; tumor cell divide to give tumor cell

• Change once occurred is self-perpetuating

• Tumor cell has uncontrolled passion for continued proliferation

Classification of tumors

• Based on the nature of tumors, they are classified as

Benign tumor – Harmless and self-limited

Malignant tumor – Harmful and rapidly growing

• Names of every tumor ends with ‘oma’

• Malignant tumor of epithelial tissue – Carcinoma

• Malignant tumor of connective tissue - Sarcoma

Classification of tumor based on tissue of origin

Tissue of origin	Benign	Malignant
Epithelial tumors
1. Squamous epithelium	Squamous cell papilloma	Squamous cell carcinoma
2. Transitional epithelium	Transitional epithelium papilloma	Transitional epithelium carcinoma
3. Glandular epithelium	Adenoma	Adenocarcinoma
4. Hepatocytes	Liver cell adenoma	Hepatocellular carcinoma (Hepatoma)

Tissue of origin (Non epithelial tumors)	Benign	Malignant
Adipose tissue	Lipoma	Liposarcoma
Fibrous tissue	Fibroma	Fibrosarcoma
Cartilage	Chondroma	Chondrosarcoma
Bone	Osteoma	Osteosarcoma
Blood vessels	Haemangioma	Angiosarcoma
Nerve cells	Ganglia Neuroma	Neuroblastoma

Contrasting features of benign and malignant tumor

Features	Benign	Malignant
Macroscopic features
Boundaries	Encapsulated/ well circumscribed	Irregular & poorly circumscribed
2. Surrounding tissues	Often compressed	Usually invaded
Size	Usually small	Often large
4. Secondary changes	Occurs less often	Occurs more often
Microscopic Features
Pattern	Closely resembles the tissue of origin	Poor resemblance to the tissue of origin
2. Basal polarity	Retained	Lost
3. Pleomorphism	Normal	Increased
Features	Benign	Malignant
Microscopic features (cont..d)
4. Neuclio- cytoplasmic ratio	Normal	Increased
Hyperchromatism	Absent	Present
Mitosis	Always typical mitosis	Atypical & abnormal mitosis
7. Tumor giant cells	May be present but with atypical nucleus	Always present with atypical nucleus
8. Cytoplasm	With normal constituents	Elements are reduced or lost
9. Functions	Usually well maintained	Retained/ lost/ abnormal
Growth rate	Usually slow	Rapid
Local invasion	Often compresses the surroundings; no invasion/ infiltration	Invade & infiltrate the adjacent tissue
Metastatis (Spreading)	Absent	Present

Structure of tumor

Tumor mass consists of:

Parenchyma
Stroma

Parenchyma

• Formed by proliferating tumor cells

• Parenchyma of benign tumor – organised pattern with resemblance to tissue of origin, differentiation

• Parenchyma of malignant tumor – unorganised, atypical, distorted, relation of tumor cell with basement is lost, anaplasia

Stroma

• Supporting tissue of tumor

• Consists of fibrous tissue carrying blood vessels for nourishing tumor cell

• More malignant the tumor, Cirrhous

• Carcinoma with scanty stroma – celluloid & medullary

• New blood vessels form from pre existing onesless is the fibrous tissue

• Carcinoma with extensive stroma – with the help of a factor, “tumor angiogenesis factor”

Spread of cancer

(Two mechanism for the spread of cancer)

Routes of spread of cancer

1. Infiltration of tissue spaces

• Tissue spaces - preformed passages; paths of least resistance

• Most vulnerable tissues – soft tissues – adipose, muscle,

• Gamete/ compact tissues like capsule of organs, cartilage and bone (not marrow) offer greater resistance

• Tissue subjected to infiltration are destroyed by the proteolytic enzymes & lytic substances elaborated by cancer tissue

• Tissue space invasion brings the tumor cell in direct contact with normal cells, lymphatic and blood vessels

2. Hematogenous spread:

• Carcinoma of lungs, thyroid, kidney and the prostate spread through blood vessels

Tumor cells enter blood stream by 2 ways

Via thorasic duct – either by perforation of vein or by lymphatic drainage
By direct invasion of blood vessels (large veins, venules & capillaries); arteries not involved due to their thick wall

3. Spread via lymphatics: Most common with carcinoma; results in both invasion & metastasis