Description
When cells in some area of body duplicate without control, the excess of tissue that develops called tumor or neoplasm. The growth of neoplastic cells exceeds and is not co-ordinated with that of the normal tissues around it. The growth persists in the same excessive manner even after cessation of the stimuli. Tumors may be cancerous and sometime fatal or they may be quite harmless. A cancerous growth is called as malignant tumor or malignancy and noncancerous growth is called as benign growth. The study of tumor is called oncology.
1 Epidemiology
With the exception rare cases, cancer
may be caused by inherited genetic defects and certain viruses. Specific cause is unknown. Several risk factors are associated with development of cancer.
All types of cancers are common, in that,
the cancer cells are abnormal and multiply out of control. However, there are often great differences between different types of cancer. For example:
• Some grow and spread more quickly
than others.
• Some are easier to treat than others,
particularly if diagnosed at an early
stage.
• Some respond much better than others
to chemotherapy, radiotherapy, or other
treatments.
• Some have a better outlook (prognosis)
than others. For some types of cancer there is a very good chance of being cured. For some types of cancer the outlook is poor.
The incidence of cancer and cancer
types are influenced by many factors such as age, sex, race, local environmental factors, diet, and genetics.
CLASSIFICATION OF CANCER
[I] Classification by Site of Origin
By primary site of origin, cancers may be of specific types like
• Breast cancer
• Lung cancer
• Prostate cancer
• Liver cancer
• Renal cell carcinoma (kidney cancer),
• Oral cancer
• Brain cancer etc.
[II] Classification by Tissue Types
Based on tissue types cancers may be
classified into six major categories:
1. Carcinoma: This type of cancer
originates from the epithelial layer of cells that form the lining of external parts of the body or the internal linings of organs within the body.
Carcinomas, malignancies of epithelial
tissue, account for 80 to 90 % of all cancer cases since epithelial tissues are most abundantly found in the body from being present in the skin to the covering and lining of organs and internal passageways, such as the gastrointestinal tract. Carcinomas usually affect organs or glands
capable of secretion including breast, lungs, bladder, colon and prostate.
2. Sarcoma: These cancers originate in
connective and supportive tissues including muscles, bones, cartilage and fat. Bone cancer is one of the sarcomas termed as osteosarcoma. It affects the young most commonly. Sarcomas appear like the tissue in which they grow. Other examples include
Chondrosarcoma (of the cartilage),
Leiomyosarcoma (smooth muscles), Rhabdomyosarcoma (skeletal muscles), Mesothelial sarcoma or mesothelioma (membranous lining of body cavities), Fibrosarcoma (fibrous tissue), Angiosarcoma or hemangioendothelioma (blood vessels),
Liposarcoma (adipose or fatty tissue), Glioma or astrocytoma (neurogenic connective tissue found in the brain), Myxosarcoma (primitive embryonic
connective tissue) and Mesenchymous or mixed mesodermal tumor (mixed connective tissue types).
3. Myeloma: These originate in the
plasma cells of bone marrow. Plasma cells are capable of producing various antibodies
in response to infections. Myeloma is a type
of blood cancer.
4. Leukemia: This group of cancers are
grouped within blood cancers. These
cancers affect the bone marrow which is the
site for blood cell production. When
cancerous, the bone marrow begins to
produce excessive immature white blood
cells that fail to perform their usual actions
and the patient is often prone to infection.
Types of leukemia include:
• Acute myelocytic leukemia (AML)
• Chronic myelocytic leukemia (CML)
• Acute lymphatic, lymphocytic, or
lymphoblastic leukemia (ALL)
• Chronic lymphatic, lymphocytic, or
lymphoblastic leukemia (CLL)
• Polycythemia vera or erythremia
5. Lymphoma: These are cancers of the
lymphatic system. Unlike the leukemias,
which affect the blood and are called “liquid cancers”, lymphomas are “solid cancers”.
These may affect lymph nodes at specific sites like stomach, brain, intestines etc. These lymphomas are referred to as extranodal lymphomas.
Lymphomas may be of two types –
Hodgkin’s lymphoma and Non-Hodgkin’s
lymphomas. In Hodgkin lymphoma there is characteristic presence of Reed-Sternberg cells in the tissue samples which are not present in Non-Hodgkin lymphoma.
6. Mixed types: These have two or
more components of the cancer. Some of
the examples include mixed mesodermal tumor, carcinosarcoma, adenosquamous carcinoma and teratocarcinoma. Blastomas are another type that involves embryonic tissues.
Central nervous system cancers:
Cancers that begin in brain tissue or the
spinal cord are known as central nervous system cancers. Primary brain tumors develop in the brain. If the tumor began in another part of the body but spread to the brain, it is called a secondary brain tumor or brain metastases. The most common type
of brain tumour develops from glial cells and is called glioma.
[III] Classification by Grade
Cancers can also be classified according
to grade. The abnormality of the cells with respect to surrounding normal tissues determines the grade of the cancer.
Increasing abnormality increases the grade, from 1–4. Cells that are well differentiated closely resemble normal specialized cells and belong to low grade tumors. Cells that are undifferentiated are highly abnormal with respect to surrounding tissues. These are high grade tumors.
• Grade 1: Well differentiated cells with
slight abnormality.
• Grade 2: Cells are moderately
differentiated and slightly more
abnormal.
• Grade 3: Cells are poorly differentiated
and very abnormal.
• Grade 4: Cells are immature and
primitive and undifferentiated.
Types of Staging
Staging is done when a person is first
diagnosed, before any treatment is given.
The main types of staging are:
Clinical staging: This is an estimate of the extent of the cancer based on results of physical exams, imaging tests (x-rays, CT scans etc.), and tumor biopsies. For some cancers, the results of other tests, such as blood tests, are also used in staging.
