Stages of cancer, differentiation and staging of cancer

Cancer has a number of different stages. Following exposure to the factor that causes cancer it usually takes a long time before the cancer begins to develop.

The cells that generate cancer cells begin to divide more vigorously than usual. As the cancer progresses, tissue that has become malignant continues to alter and become more malignant. The tumour cells become differentiated and the body’s regulatory system is no longer able to control the changes taking place, and so eventually the cancerous tissue begins to spread.

Cancer begins to cause damage to the body by growing locally, metastasising in different organs and causing a variety of general symptoms. A malignant tumour can become sizeable at its primary site and harm the normal functioning of the organ in question. The tumour can also displace neighbouring organs, causing pain and pressure symptoms.

Cancer symptoms

Cancer staging and staging classifications

Cancer staging is determined in connection with detecting the disease. Determining cancer staging can be used to get an idea of the scope for recovery and to select the right sort of treatment.

Cancer staging is usually depicted using the international TNM classification

  • T refers to the size of the primary tumour
  • N denotes the extent to which the cancer has spread to regional lymph nodes
  • M refers to the existence of distant metastases

Cancer is divided into five stages using the TNM system – 0, I, II, III, IV. Stage 0 means the presence of a small carcinoma in situ that has not spread. Stage IV means cancer that has spread widely or cancer that has metastasised. In some cases the stages have subclasses.

When it spreads, cancer starts to produce metastases. These are created when cancer cells spread from the primary site via the bloodstream or lymphatic system and become attached to other organs. From there they begin to divide and invade space.

Different cancers typically metastasise in certain organs. The most common metastases occur in the liver, lungs, adrenal glands, brain and bones. The symptoms caused by metastases vary according to their location.

Cancer tissue types

Cancers are named according to the location of the primary site tumour and the structure of the tumour tissue.

The body’s normal tissue types include:

  • Epithelium (the outer layer of the skin and mucosa)
  • Supportive tissue (bone, cartilage, connective tissue, muscle tissue)
  • Nerve tissue
  • Lymphatic tissue
  • Bone marrow

The epithelium covers the whole surface of the body and wraps all of its internal surfaces and cavities. The surface of the skin, mucosa, gastrointestinal tract and bladder are exampled of epithelial tissue.  Cancer that develops from the epithelial tissue is a carcinoma.

Cancer that develops from supportive tissue is a sarcoma.

The brain, spinal cord and nerves are what make up nerve tissue. There is no general term for tumours that originate from nervous tissue. They are usually named according to the tumour tissue. The development of benign tumours in nerve tissue is common, but because of their location they can be harmful, if removing them is difficult.

Cancer that develops in lymphatic tissue is called a lymphoma, while cancer that develops from bone marrow cancer is called leukaemia.

Tumours are classified by histological type, meaning according to the type of tissue in which the tumour starts because, among other things, it affects the choice of treatment.

The table below lists benign and malignant tumours according to their histological type:

Tissue type Benign Malignant
Epithelial  
surface epithelium papilloma carcinoma
gland or duct epithelium adenoma adenocarcinoma
Connective tissue and muscles
dense connective tissue fibroma fibrosarcoma
cartilage chondroma chondrosarcoma
bone osteoma osteosarcoma
smooth muscle leiomyoma leiomyosarcoma
skeletal muscle rhabdomyoma rhabdomyosarcoma
Nerve tissue
glial tissue glioma glioblastoma
meninges meningioma meningeal sarcoma
retina retinoblastoma

Cancer differentiation

Cancer differentiation grades refers to the graded classification of tumours, according to how differentiated the tumour is. Usually there are three or four grades.

There are differences in cancer differentiation. A tumour that closely resembles the structure of the tissue it started in is described as very differentiated. Thus, the closer the structure of the cancer cell is to that of a normal cell structure, the better it is differentiated. A tumour that resembles the original tissue to a lesser extent is termed poorly differentiated, or anaplastic.

When cancer cells are poorly differentiated, it can complicate identifying the tissue they started in and targeting treatment.

Many tumours are divided into three grades of differentiation.

Cancer differentiation grades

Well differentiated, Grade 1

  • Mostly resembles normal tissue and usually has a good prognosis

Moderately differentiated, Grade 2

  • Intermediate forms of tumour with both good and bad prognosis

Badly differentiated, Grade 3 and undifferentiated, Grade 4

  • Tumours spread easier than other tumours, and their prognosis is a little worse than for others.

The grading criteria vary in tumours in different organs and in different types of tumour. The general rule is that well-differentiated tumours behave more calmly than badly differentiated tumours. Grading is used when assessing the need for post-operative medical treatment.

Sources

Joensuu, Heikki; Jyrkkiö, Sirkku; Kellokumpu-Lehtinen, Pirkko-Liisa; Kouri, Mauri; Roberts, Peter J. & Teppo, Lyly (toim.) (2013) Syöpätaudit. Helsinki: Kustannus Oy Duodecim