The following points highlight the top three types of abnormalities found in cancer cells. The types are: 1. Morphological Abnormalities of Cancer Cells 2. Chromosomal Abnormalities of Cancer Cells 3. Biological Abnormalities of Cancer Cells.
Abnormalities found in Cancer Cells: Type # 1.
Morphological Abnormalities of Cancer Cells:
(i) Rounding up of Cell Shape:
Cancer cells are more rounded in shape than their normal counterparts.
(ii) Changes in Nucleus:
The nucleus and nucleolus are much bigger in size than that of normal cells and the nuclear outline is irregular. In other words the nucleocytoplasmic ratio is higher than normal.
(iii) Cytoplasmic Changes:
Cytoplasm may show granular inclusions such as milk droplets in mammary tumors, melanin granules in malignant melanoma and mucus droplets in gastric cancer. On the other hand, microtubules and microfilaments become reduced in the cytoplasm of T-cells.
(iv) Change in Plasma Membrane:
Plasma membrane of many transformed cells shows ‘blebs’ and minute vesicles. New antigens are added to the plasma membrane of cancer cells, for example, colon and breast cancer cells develop new antigens, CEA (carcinoembryonic antigen) on their surface. Change in surface charge and increase in surface protease (plasminogen activator) are also shown by cancer cells.
Abnormalities found in Cancer Cells: Type # 2.
Chromosomal Abnormalities of Cancer Cells:
Often, the cancer cells have a higher than normal chromosomal number or the cancer cells are often found to be aneuploid. For instance, human uterine cervix cancer cells often show trisomy of chromosome number 1 and Burkitt’s lymphoma cells often show trisomy of chromosome number 14.
Structural aberrations of chromosomes are also frequently found in cancer cells. Chronic myeloid leukemia cells contain an unusually short chromosome number 22 (from which a part was trans-located to chromosome number 9). It is called as Philadelphia chromosome.
Abnormalities found in Cancer Cells: Type # 3.
Biological Abnormalities of Cancer Cells:
(i) Uncontrolled Proliferation and absence of Differentiation:
Cancer cells proliferate in an uncontrolled manner and at an exponential rate. They proliferate so fast that they do not have the time to undergo differentiation. So they remain in an undifferentiated state that is called anaplasia.
(ii) Loss of Contact Inhibition:
Normal cells when put in culture, stop movement whenever they come in contact with one another or in contact with the glass surface (culture pot). This is called contact inhibition.
Lackie in 1985 held that mutual contact between cells in culture causes rapid changes in the organisation of actin-based cortical cytoskeleton of cells, which stops cell movement. The cancer cells, on the other hand, are incapable of forming the stress fibre of actin filament and thus do not show contact inhibition.
(iii) Metastasis:
Normal cells remain tightly adhered to one another to form a compact tissue. On the other hand, cancer cells often lose adherence with neighbouring cells, invade through walls of capillaries or lymph vessels (Fig. 3.39) and migrate to secondary foci to form secondary tumors.
This power of spreading from primary focus to secondary foci through blood vessels or lymph vessels is called metastasis.
McCarthy et al. (1988) have held that at least three factors cause metastasis:
(a) Cancer cells have reduced adhesiveness as they lose cadherin, talin, fibronectin etc. molecules that help in cell-to-cell adhesion in case of normal cells,
(b) Cancer cells also show marked changes in some other surface-glycoproteins which result in the formation of several laminin- receptors on their surface. By these receptors, cancer cells bind to the laminin protein in the basement membrane of capillary walls,
(c) Finally, cancer cells secrete type IV collagenase that creates holes in the capillary wall for the entry of the cells into the capillaries.
(iv) Angiogenesis:
Cancer cells show the ability to trigger the blood vessels to grow towards them for the supply of blood.
(v) Reduced Nutrient Requirement:
Cancer cells have reduced requirement for extracellular growth factors, but these cells may show some specific growth factors that stimulate their own proliferation — a characteristic called autocrine growth stimulation.
(vi) Loss of Cell Death:
Cancer cells are less sensitive to toxin, x-ray and induced programmed cell death (PCD) or apoptosis.