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:

1. Parenchyma
   

2. 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

1. Via
   thorasic duct – either by perforation of vein or by lymphatic drainage

2. 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

Spread via lymphatics

Lymphatic
spread begins by lodgement of tumour cells in subcapsular sinus via afferent
lymphatics entering at the convex surface of the lymph node

Hematogenous spread

4. Spread via serous sacs

•       Spread
through peritoneal cavity; common in cancer of GIT & ovary

•       Trans
pleural spread –  in carcinoma of lungs
and breast

•       Trans
pericardial spread may also occur

5. Spread along epithelium line surfaces

•       Intact
epithelium, mucous coat acquires resistance for penetration of  tumor

•       Implantation
tumor – tumor spread along the surface of epithelium

6. Spread via CSF

•       Cerebrospinal
cavities are affected by the escape of tumor cells from

•       the
malignant tumor in the brain or meninges

Summary

•       A tumour is a mass of tissue formed
as a result of abnormal, excessive, uncoordinated, autonomous and purposeless
proliferation of cells

•       Tumors
are classified as benign and malignant

•       Benign
tumors are harmless and do not spread while malignant tumors are harmful and
spread

•       Tumor
is made up of parenchyma and stroma

•       Tumor
spread by two mechanism – Haematogenous spread and lymphatic spread