HOW CANCER GROWS

DNA or Deoxyribonucleic Acid is the genetic material that resides in a cell. DNA in fact is a code that carries all the information required for the cell to multiply and perform its intended function. Sometimes due to certain changes (mutations) to the DNA, normal cell growth and division is affected. This forms the origin of cancerous growth in the body as these abnormal cells with mutated DNA do not stop reproducing. In fact, as the mutated cell produces more cells, it replicates the mutated DNA in each new cell it creates. This process continues with a cluster of mutated cells and a tumour begins to form. A single mutation, however, does not lead to a cell being termed cancerous. It can take a mutated cell several more mutations before it can be classified as being cancerous.

How cancer grows

In order to sustain their growth, these cancer cells need a supply of oxygen and nutrients like all normal cells. Without their own blood supply to nourish them, tumours cannot grow large. As a tumour grows, it sends out chemical signals to nearby blood vessels in an attempt to hijack the blood supply. Responding to these signals, new blood vessels begin to grow towards the tumour which aids its nourishment. This process is called angiogenesis.

As a tumour gets bigger, it takes up more and more room in the body while pressing on the normal body tissue nearby. The tumour then attempts to force itself through the normal tissue in order to permeate the neighbouring tissue. In this process it squeezes and blocks small blood vessels in the area. Due to starvation i.e. low blood and oxygen levels, some of the normal tissue begins to die which makes it easier for the cancer to continue its growth.


With growth and spread being their main purpose, the cancer cells break away from the original primary tumour and begin their journey through the bloodstream and the lymphatic system. This is in fact the cancer cells’ super highway! The cancer cells then travel to attach themselves to other parts of the body and then begin to grow in their new found location. While the cancer that grows where it first started is called the primary cancer, the cancer that grows from the place it has spread to is called the secondary cancer. The spread of cancer from one part of the body to another is called metastasis.

 
Classifying cancer growth

There are two ways in which cancer growth in the body can be described:


  • Cancer Grading    -    How abnormal the cancer looks
  • Cancer Staging    -    How the cancer is progressing through the body

Cancer Grading
Grading is used to classify cancer cells in terms of how abnormal they look under a microscope and how quickly the tumour is likely to grow and spread. In general, a lower grade indicates a slower-growing cancer and a higher grade indicates a faster-growing one.

Based on the microscopic appearance of cancer cells, pathologists commonly describe tumour grade by three degrees of severity: Grades 1, 2 and 3. The cells of Grade 1 tumours resemble normal cells, and tend to grow and multiply slowly. Grade 1 tumours are generally considered the least aggressive in behaviour. Conversely, the cells of Grade 3 tumours do not look like normal cells of the same type. Grade 3 tumours tend to grow rapidly and spread faster than tumours with a lower grade.

Grading classification corresponds to one if three grades.

Grade Definition
G1 Well-differentiated (Low grade)
G2 Moderately differentiated (Intermediate grade)
G3 Poorly differentiated (High grade)

Cancer Staging
Staging helps estimate a person’s prognosis. Staging is defined based on the way a cancer progresses in an individual. It describes the severity of a person’s cancer based on the extent of the original (primary) tumour and whether or not the cancer has spread in the body.

Staging allows doctors to:

  • work out how large the cancer is
  • understand the extent of the cancer’s spread
  • estimate prognosis and the best treatment options possible

Staging is mostly described using the TNM system. TNM stands for Tumour, Lymph Node, and Distant Metastasis.

  • ‘T’refers to the size of the tumour
  • 'N' refers to whether the cancer has spread to the regional lymph nodes
  • 'M' refers to whether the cancer has spread to another part of the body i.e. distant metastasis

Several combinations of T, N and M are possible.

Stage Definition
Stage 0 Carcinoma in situ (Cancer cells have not invaded below the surface layer in which they have developed). In this stage cancer will not have spread anywhere else and can be treated by local excision.
Stage I, II and III Higher numbers indicate more extensive disease: Larger tumour size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or organs adjacent to the location of the primary tumour.
Stage IV The cancer has spread to another organ(s).