| Carcinoma | |
|---|---|
| Classification and external resources | |
| OMIM | 8010/3 |
| MeSH | D002277 |
Carcinoma is a medical term that refers to an invasive malignant tumor consisting of transformed epithelial cells. Alternatively, it refers to a malignant tumor composed of transformed cells of unknown histogenesis, but which possess specific molecular or histological characteristics that are associated with epithelial cells, such as the production of cytokeratins or intercellular bridges.
Carcinoma in situ (CIS) refers to a small, localized focus of carcinoma that has not yet invaded through the epithelial basement membrane that delimits the carcinoma cells from the adjacent normal tissue. It is important to remember that carcinoma in situ is a pre-invasive cancer, and not a "pre-malignant" entity.[1] In most cases, CIS will progress to an invasive carcinoma unless it is completely removed via surgical resection, cryotherapy, or some other treatment modality. In some instances, however, CIS can regress and even disappear, a phenomenon often linked to negation of the original carcinogenic stimulus (i.e. smoking cessation, clearing of HPV virus).[2]
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Malignant neoplasms are exceptionally heterogeneous entities[3] and, to date, no simple comprehensive method for classifying them has yet been devised.[4] Traditionally, however, malignancies have been generally been classified using a combination of criteria, including:[5]
Adenocarcinoma refers to a carcinoma that produces glands and/or mucin.
Squamous cell carcinoma features intercellular bridges, keratinization, squamous pearls, or other characteristics of squamous differentiation.
Some carcinomas have monotonous appearing cells that lack histological or cytological evidence of more specifically differentiated neoplasms. These tumors are referred to as anaplastic, or undifferentiated, carcinomas. In the lower respiratory tract, examples include large cell lung carcinoma, small cell lung carcinoma, and pleomorphic carcinomas[6]. The latter have anaplastic cells that may be spindle-shaped (spindle cell carcinoma, or contain multinucleated giant cells (giant cell carcinoma), and may contain components of more differentiated tumor tissue. Rarely, tumors may contain components of both carcinoma and sarcoma, for example the carcinosarcomas.
Sometimes a tumor is referred to by the presumptive organ of the primary (eg carcinoma of the prostate) or the putative cell of origin (hepatocellular carcinoma, renal cell carcinoma).
"Metastatic carcinoma" refers to tumors that have metastasized, or spread, from another "primary" site to the site at which the tumor is located. These can be diagnosed through biopsy, including fine-needle aspiration (FNA), core biopsy, or subtotal removal of single node.[7]
(8010-8790) Epithelial
The staging of cancers is the extent of spread of the neoplasm. Grading is the system used to record the tumors degree of differentiation from the parent tissue. High grade lesions shows little differentiation and may convey a worse prognosis depending on tumor type. As a general rule, cancer stage (using AJCC criteria) dictates ultimate prognosis. The criteria for staging differ based on organ system. For example, the colon and bladder cancer staging system relies on depth of invasion. Breast and lung staging is more dependent on size. While renal carcinoma staging is based on both size and invasion into the renal sinus. Accurate staging is reliant on clinical, radiographic, and pathologic data. The UICC/AJCC TNM system is often used, however for some common tumors, classic staging methods (such as the Dukes classification for colon cancer) are still used.
Many people get frightened when they hear the word cancer. Cancer unfortunately is a common illness in our society. Cells in almost every part of the body can become cancerous. While cancer is a disease of old age, children can also develop certain cancers. [8]
There are many types of cancers that affect different parts of our body. While we do know what causes some cancers, (e.g. sun causes skin cancers or that smoking can cause lung cancers), for the vast majority of cancers the cause remains unknown. All we know is that cancers represent cells that have lost the ability to die and continue to proliferate. When these cells continue to multiply and proliferate, they overcome the normal bodily functions, compress organs, invade other tissues and ultimately cause death. However, even among cancer cells there is a large variation. Some skin cancers will remain localized and not spread (e.g. basal cell carcinoma), whereas others like melanomas do tend to spread very quickly. The faster a cancer spreads the worse the prognosis.
When an individual is diagnosed with a cancer, the report often says that the cancer is well differentiated or poorly differentiated. [9] These words have significant impact on prognosis. Well differentiated cancer means that when analyzed under a microscope, these cancer cells look very much like normal cells and have the same cellular contents but have genetic machinery which tells them to divide fast. Undifferentiated or poorly differentiated cancers cells look very primitive and do not resemble normal cells at all. In general, well-differentiated cancer cells behave in some type of organized fashion and have a vastly better prognosis compared to poorly differentiated cancer cells. Cancer cells, which are poorly differentiated, have no control over growth, randomly spread and invade all surrounding and distant tissues. Why one cancer is well differentiated and other is poorly differentiated in the same organ remains unknown.
When a cancer is diagnosed, the tissues are studied in the laboratory for many features to determine their genetic makeup, degree of differentiation and cancer marker genes. Cancers are generally graded on how they look under a microscope. Grade 1 cancers are well differentiated, grade 2 are moderately well differentiated and grade 3 are poorly differentiated cancer cells. The higher the grade, the worse the prognosis [10]
Any normal cell has the potential to become cancerous. All normal cells in the body have the ability to stop growing when they come into close contact with each other. The cell's genetic program senses the contact and this is how normal growth is regulated. In cancer cells, this ability to stop growing when coming into contact is absent and thus, the cancer cells keep on growing and become autonomous. The other property of cancer cells that makes them different from normal cells is that they become immortal. All normal cells are programmed to die at a certain point in their lifetime. Cancer cells somehow lose their "death" program and live indefinitely- this means once a cancer has started, it never stops growing. [11]
Poorly differentiated cancer cells can easily be recognized under a microscope. For example, a cancer of the skin may have cells that look bizarre, have abnormal nuclei and large amount of genetic material and few very organized features. These cells do not become specialized and just keep on multiplying. Once the cancer cells reach a critical mass, they break off and spread to other parts of the body where the cycle of growth and spread continues. Eventually cancer spreads in the entire body. Well-differentiated cancer cells look like normal cells and do have some functions that are similar and hence these cancers do respond to anti cancer drugs or radiation therapy. On the other hand, poorly differentiated cancers act autonomously and very rarely respond to any drug or radiation treatment. [12]
Some of the cancers which tend to have poorly differentiated cells include thyroid, colon, squamous cell, small cell cancers of the lung, ovarian cancer, head and neck cancers. In all cancers, the earlier the diagnosis is made, the better the prognosis.
Based on the degree of differentiation and other features of the cell, physicians can sometimes predict with some degree of accuracy, the response of the cancer to anti cancer drugs and life expectancy.
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