The Tumor is known as an excessive and unnatural growth. But the standard definition of tumor is not known that much. Tumor or neoplasm is defined as the abnormal, excessive, uncoordinated, autonomous, and purposeless growth of cells. The specialty is that the growth doesn’t stop even after the causative agent has been removed. Remember this definition with PAUsE!

P- Purposeless

A- Abnormal & Autonomous

U- Uncoordinated

E- Excessive

This growth is called neoplasia and the resultant cells are called tumor or cancer or neoplasm. The following are the differences between a normal cell and a tumor.

Broadly, there are two reasons for this to occur, genetic changes and substances.

Genetic changes

  • Mutation in DNA
  • Non-lethal but passed onto daughters
  • Multiple alterations in gene
  • Intrinsic and extrinsic inheritance

Carcinogen – the substance that induce cancer

The carcinogenic substance can be chemical, physical, or infectious in nature. Based on the rate of growth and proliferation, tumors are of two types, namely benign and malignant. The following highlights the difference between them.

Cancer can occur in different regions of the body. Naming them is of importance so medical professionals can evaluate the condition. There is a nomenclature for benign and malignant tumors.

Benign tumors end with -oma.
Represented as origin+morphology+oma.

An example is an epithelioma (squamous epithelium). If the malignancy occurs in mesenchymal tissues, it ends with sarcoma. Whereas if it occurs in epithelial tissues, it ends with carcinoma (adenocarcinoma). Teratomas and hamartoma are certain mixed tumors.

Different types of cancer

Malignant cells spread and infect the normal cells and they also spread to distant regions by a process called metastasis, also called the indirect spread. There are 8 significant events in metastasis.

Significant events in metastasis

  1. Aggressive clonal proliferation and angiogenesis. The tumor cells proliferate aggressively with the formation of new blood vessels to supply nutrients.
  2. Loosening of tumor cells. The tumor cells detach due to the inactivation of CAM (Cell Adhesion Molecules).
  3. Interaction with ECM. Loss of integrin, a CAM favors invasion.
  4. Degradation of ECM. The tumor cells release protease and other enzymes that degrade the ECM, exposing the tumor cells to capillaries.
  5. Entry into capillaries. This is also called intravasation and is stimulated by AMF (Autocrine Motility Factor).
  6. Thrombus formation. The newly entered tumor cells react with immune cells. Since they outnumber them, they form emboli that nourish and protect other tumor cells.
  7. Extravasation. These cells travel through the capillaries and exit the bloodstream when they reach a new target location. The enzymes degrade the endothelium and ECM.
  8. Survival and growth. This is then followed by proliferation and angiogenesis. This can undergo further metastasis also in the future.

Apart from metastasis, the other characteristics of tumor cells are mentioned as follows.


  • Rate of growth. more proliferation with increased doubling time.
  • Degree of differentiation. Inversely proportional to the rate of growth.
  • Immortality. Escape from death signals.
  • Unstable. Presence of newer mutations and rapid growth.
  • Invasion. Also called the direct spread. Benign cells don’t infiltrate and invade other cells whereas malignant cells do.

There are different stages and grades in a tumor. Grading is based on the degree of differentiation and anaplastic cell content. It ranges from grade 1 to 4 with increasing concentrations of anaplastic cells.

The systems used to stage them are TNM and AJC. T is the size of the tumor; N is the node (local/regional) and M is the metastasis. Numbering from 0to4 indicates the severity of the condition.

T1N0M0 refers to small localized tumors whereas T4N3M3 refers to the very large tumors with regional node and distant metastasis.

AJC divides cancers into 4 stages based on T, N, and M.


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