What's cancer?

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Although initially this seems like a simple question, the term is actually quite difficult to define. Cancer usually refers to an abnormal invasive growth of tissues that is uncoordinated with the function of surrounding tissues caused by genetical changes. It is also commonly used to describe the disease which is caused by these growths. The word cancer actually originates from the greek for crab, Hippocrates was the first to use this word to describe cancerous growths due to the finger like growths cancerous cells cause. 



Cancer describes a particular type of abnormal growth of tissues, however many terms commonly used in describing cancers are not necessarily synonymous, this includes words such as; 


Tumours 
Neoplasia
carcinoma


There are also many types of abnormal growths which may not necessarily be cancer; 


Hyperplasia
Hypertrophy
Dysplasia
Benign neoplasia
Malignant neoplasia


So what are the differences between these terms? How do we define what is a benign neoplasia and what's a malignant neoplasia? Can Benign growths become malignant? 



Tumors

A tumor simply refers to a swelling- this may be due to (a) normal physiological changes such as a baby, caused by (b) physiological changes due to disease such as a callus formed after a fracture, or pus filled pustules or caused by (c) abnormal new growths. The Greek physician Galen used the word ‘onco’ to describe tumors, which is where words like oncology come from. The word tumor now tends to only be used to describe neoplastic growths. Also not all neoplasms present as a lump and therefore not all neoplasms are tumors.

Neoplasm
A neoplasm is a new growth which: 
  • Exceeds the growth of normal tissues.
  • Is uncoordinated in function with surrounded tissues.
  • Continues growing even when stimuli that caused it to grow in the first place is withdrawn.
  • Is caused by genetical changes that are heritable by daughter cells.
Neoplasms often contain multiple cell types but usually originate from a single group of identical cells. Theoretically, a group of neoplastic cells should be genetically identical and this characteristic is called clonality.
Neoplasm may be benign, premalignant or malignant.

Difference between benign and malignant neoplasms
The main difference between benign and malignant neoplasms is their abilities to invade other surrounding tissues and to metastasize and spread to other parts of the body. Benign tumors also tend to be well circumscribed, and slow growing, with cells which are similar to those of the original tissue. Malignant growths often form finger like projections into the surrounding tissues and their rate of growth varies. 

Both malignant and benign growths can cause disease. Malignant growths disrupts the normal function of organs and cause what we commonly know as cancer. Benign growths however may not cause harm at all or may cause disease by compressing on various structures in the body. For example, a meningioma – a benign tumor from the coverings of the brain, may cause disease by compressing the brain.

It is uncommon for most types of benign growths to become cancerous, however certain types of benign growths are also more likely to become malignant if they gain additional genetical changes. Certain types of neoplasms are known to frequently malignant although they are by definition benign. This includes certain types of gastric polyps such as adenomas. Although adenomas will not necessarily become malignant, a portion of them will become invasive and most malignant cancers of the gut arises from these.  


Benign neoplasms
Premalignant
Malignant



Benign lipoma- A tumor of fatty tissue, which commonly develops amongst people between 40-60.


Premalignant cells in cervical cancer (also known as carcinoma insitu) where cells have not invaded into the lower levels of the cervical wall









basal cell carcinoma of the skin- the growth is poorly circumscribed,


Other terms defining abnormal growth

A number of terms may be used to describe growth of tissues which may or may not be related to neoplasias.

  • Hypertrophy – The growth of a tissue due to increased cell size and organelles rather than increased cell numbers. Occurs to cells that have a low turnover rate or do not replicate, for example neurons or heart muscle.
  • Hyperplasia- The increase in tissue size due to increased cell numbers.
  • Aplasia –The defective development of a certain tissue, which should exist.
  • Metaplasia – The replacement of one mature cell type with another usually due to changes in the environment- i.e. Tissues which are constantly or repeatedly irritated.
  • Dysplasia- A change in tissue structure/organisation, shape, or size in metaplastic or hyperplastic tissues. This is commonly caused by genetical changes.  Dysplasia may be reversible
  • Anaplasia – The reversion of a tissue to a less mature/undiffrentiated form, this may occur in some malignant growths.

Describing tumors
When describing tumors, it is important to determine;
  • Is it benign or malignant?
  • Is it primary or secondary?
  • If it is secondary where does the tumor originate?

References
http://www.cancer.org/Cancer/CancerBasics/TheHistoryofCancer/the-history-of-cancer-what-is-cancer
http://www.pathguy.com/lectures/neo-1.htm#intro
https://www.meducation.net/community_notes/10066
http://www.ncbi.nlm.nih.gov/books/NBK6994/

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