Cancer cells
come in many general types and countless varieties, and each sort generally shares many characteristics with a healthy cell of its kind. For example, cancerous epithelial skin cells often have similar physical and biochemical characteristics as normal skin cells. Therefore, it is difficult to assign certain "cell structure" properties to cancerous cells in general. However, we can describe several key components that can be found in most malignant tissues.
Benign vs. Malignant Tumors
Cancerous cells can be defined by two key properties. First, they are able to reproduce at an abnormal rate by overcoming normal cell proliferation "checkpoints." Second, cancer cells have the ability to invade areas away from their origin and create secondary tumors known as "metastases." This is the essence of the difference between benign and malignant tumors; malignant cancers can spread to surrounding tissue and colonize those areas, increasing their own growth while often damaging surrounding healthy tissue. Generally, the more metastasis that occurs, the harder it becomes to eliminate the cancer.
Cancer Cell Types
There are three general cancer cell types, and these are categorized according to the original tissue the cancer started in. Carcinomas are cancers that develop from epithelial cells, from the outer layer of a membrane (such as skin cells). Tumors arising from muscle or connective tissue are called sarcomas. The third category actually covers the types of cancer that do not arise from either of the first two groups; this includes leukemias and nervous system cancers, among others. Cancer cells often retain many of the properties of their healthy counterparts. For example, melanoma (skin cancer) cells usually continue making pigment molecules even after they have become cancerous.
Tumor Progression and Metastasis
Tumor progression is the overall process by which an initially small problem of cell behavior gradually turns into a fully advanced cancer. Throughout this process, the cells of a tumor can vastly change in size, shape, internal structure, and biochemistry. In order for an initial tumor to metastasize and colonize another area of the body, it must first break through the basement membrane of a tissue, known as the "basal lamina," and enter the bloodstream by crossing the wall of either a blood or lymph. For a tumor to get through the basal lamina, it must first change its cell structure so that it may connect to the membrane and digest it with an enzyme such as type-IV collagenase.
Dysplasia
One key occurrence in several cancers, such as those of the uterine cervix, is the presence of dysplasia; there is some kind of disorder in the cell differentiation and release processes. Normally in the uterine cervix, undeveloped cells will first differentiate into their programmed cell types near the basal layer of the tissue, and only then will they be dispatched to the rest of the organ to perform their functions. However, when dysplasia occurs the cells are released in abnormally early stages of their development. While most of the time this does not result in anything harmful, in certain instances these underdeveloped cells can start to grow incorrectly and form a dangerous tumor growth.
Examples of Structural Changes in Cancer Cells
In Paget's carcinoma, the epidermis (outer layer) of the breast is invaded by cancer cells coming from deeper down in the organ. These cancer cells have several visible differences compared to healthy breast epidermal cells, such as variably shaped and excessively large nuclei, along with a halo of clear space that surrounds each cancer cell.
In another example, healthy connective tissue cells generally have a flattened appearance, as they are connected to other cells and intercellular networks by tethering-type proteins. However, once a Rous sarcoma virus invades and transforms these cells, they take on an abnormal rounded shape and lose their adherence to their surroundings, also gaining the ability to grow uncontrollably and spread.
Tags: skin cells, basal lamina, cancer cell, cancer cells, cancer cells
