The pathological path for cancers is the abnormal proliferation of cells different in type, numbers, and actions of otherwise normal cells for the tissue or organ system in question. The growth of cells can be rapid or slow. Cell accumulation can be minuscule or massive. The ultimate clinical criteria for a cancer diagnosis are that the cells in question are distinctly different (microscopically and macroscopic) from the ordinary evolution, appearance, and proliferation of cells.
As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed forming growths called tumors. Many cancers form solid tumors, whereas cancers of the blood, such as leukemias, generally do not form solid tumors. Cancerous tumors are malignant and can spread into, or invade nearby tissues (Blog #27, Tables 6.1 and 6.2). Some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. A cancer that has spread from the place where it first started (primary site) to another place in the body is called metastatic cancer. Diagnostic tests ranging from laboratory studies to imaging to biopsy are all clinically indicated in a cancer diagnosis (Table 6.3).
Cancer cells are also often able to evade the immune system’s organs and cells. Some cancer cells are able to “hide” from the immune system (see PDL-1 ligand under CRISPR). Tumors can also use the adaptive immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can sometimes prevent the immune system from killing cancer cells (a deadly paradox).
Cancers are identified by the type of cells involved and the area of the body from where they originate. The first diagnostic tests in a cancer diagnosis include biopsy and imaging ranging from photography, through nuclear scanning, and MRIs. Other more advanced diagnostic tests include transcriptomics (the study of gene protein expression) and proteomics (the molecular biology of the expressed proteins) to establish diagnostic markers for more accurate diagnoses of cancers. Using global DNA gene expression data derived from epigenetic experiments, genomic sequencing is now involved in cell type-specific regulation of gene expression. Computerized artificial intelligence (AI) image analysis that can identify different types of cancer cells simply by scanning microscopic images is now being used extensively in cancer diagnosis.
Besides determining the nature and type of cancer in a diagnosis, one of the most critical considerations in the clinical presentation is “staging.” This is a determination of how advanced the cancer is relative to its spreading (metastasis) beyond its original location. To determine this, a number is assigned (I through IV) to characterize the degree of spread (from local to disseminated, i.e., to other tissues and/or organ systems beyond the original site). The higher the number, the more cancer has spread locally or throughout the body. This information is critical in determining a plan of treatment.
Discussion Questions:
Some cancer cells are able to “hide” from the immune system. How does the PD-1 ligand and T cells accomplish this “trick?”
Cancers are graded by “staging” from I through IV. Can you explain how this staging is determined?
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