Histology of Cancer
1. Transformation of a single cell, termed the target cell
2. The transformed cell has a selective and growth advantge over its surrounding cells, and begins to grow
3. Grow exceeds its confines, and local invasion begins
4. Distant metastses subsequently develop
Differentiation is a term that describes how much a cell resembles a normal cell. Resemblence in both morphology and functional capacity is used. Cell that do not resemble any cell, look in general similar to primitive cells, are termed anaplastic. This is in comtrast to well-differentiated cells that look similar to cells from the original tissue. This is most common with benign tumors. With anaplastic tumors, also termed poorly or undifferentiated tumors, the cells appear primitive, small, and unspecialized. The peculiar aspect of cancer cells is that they can range from these extremes. Simply, the can either be well-differentiated malignancies or undifferentiated mallignancies, but also lie somewhere in between. Undifferentiated cancer cells, are usually termed anaplastic. These cells define the main aspect of cancer, which is transformation. It was initially believed that anaplasia meant going backwards in time towards a more primitive cell, however, recently it is believed that anaplasia means cancer of a tissues regenerating capacity stem cells.
Anaplasia is just one aspect of cell differentiation and histology that can be characteristic of cancer cells.
Pleomorphism is a term that describes variation in size and shape of cells and their nuclei. Usually there is no variation in cells.
Nuclear morphology abnormalities describe hyperchromatic nuclei, which means dar-staining, due to the high binding of basic dye to the acidic chromosomes. Basophilic, (philos, attraction, to basic) as chromatin binds hematoxylin. Moreover, nuclei are seen to be very large in comparison to the cytoplasm that surrounds them. Like pleiomorphism, the nuclear shape is irregular and the chromatin is found mainly at the borders of the nuclear membrane. Nucleoli are also usually large in comparison to normal cells. These are changes which one would see with rapidly dividing and growing cells that are producing increasing levels of protein and mRNA to sustain rapid growth.
Mitoses are a common feature of tumor cells, and can easily be seen on histology, making them prime targets for the eye. These mitoses can also be seen in normal tissues, so it is the number of mitoses, their location (e.g., uppder layers of the skin, whereas they should be only found in the lower levels) and the appearance of any abnormal mitotic processes, such as tripolar or multipolar spindles.
Loss of Direction of cell growth is also seen with anaplasia, where cells begin growing in any direction.
Tumor giant cells can also be seen in cancer, however, these are in contrast to viral infected or macrophage derived giant cells, which have small nuclei, cancer giant cell nuclei are large and hyperchromatic.