Carcinoma is the most common type of cancer in humans, and it can appear in virtually every tissue in our body. We call carcinoma the cancer that originates from an epithelial tissue, that is, the tissue that covers our skin and most of our organs.
As the carcinoma arises from an epithelial cell, it is important to understand a little what these cells are.
The human body is composed of basically four types of tissues:
Connective tissue
Nervous tissue
Muscle tissue
Epithelial tissue
The epithelial tissue, formed by epithelial cells, is distributed diffusely by our organism as it is responsible for the coating of our skin's organs. The epithelial tissue is like a cover that covers and protects our organs. The most superficial layer of the skin, called the epidermis, is composed only of epithelial cells.
There are several different types of epithelial cells, several of them with functions other than just coating and protecting organs. For example, in the epithelial tissue of the intestines there are epithelial cells capable of absorbing nutrients; in the mouth there are epithelial cells capable of recognizing flavors; the same occurs in the inner lining of the nose, where neuroepithelial cells recognize odors.
There are also epithelial cells that have glands, being able to secrete substances such as saliva in the mouth (salivary glands), fat and sweat in the skin (sebaceous and sweat glands), milk in the breasts (mammary glands) and acid in the stomach (parietal cells).
Therefore, each organ, including the skin, has its own epithelial tissue, often composed of more than one type of epithelial cell, each with a different function in the organism.
All of our cells have a shelf life, being destroyed when they become old or when they suffer irreparable damage to their structure. Our body is programmed so that only healthy cells survive. If any cell undergoes alteration of its DNA, it automatically destroys itself in a process called apoptosis. Apoptosis is a defense mechanism that nature has developed to prevent cells with compromised DNA from multiplying.
We have genes, called proto-oncogenes, whose function is to control the process of apoptosis and prevent the onset of cancer cells. You may not know it, but all the time there are cells with cancerous potential in your body that do not turn into cancer because of the defense mechanisms your body possesses.
Skin cancer, for example, arises when a cell in the epithelium of the skin, after prolonged sun exposure, undergoes a mutation of its DNA due to the deleterious actions of ultraviolet rays. If the apoptosis mechanism does not work, the mutant cell will not be eliminated and will act on its own, doing things that a normal skin cell does not do, such as forming new tissues, invading other organs, growing and multiplying uncontrollably.
Carcinoma is the type of cancer that arises when any epithelial cell undergoes malignant transformation. For example, if the mutated cell is a kidney epithelial cell, the cancer that arises from it is renal cell carcinoma; if the cancer origin is the epithelial cell of the liver, known as hepatocyte, the cancer will be called hepatocarcinoma.
Not all carcinomas have their origin easily recognized. Some of them suffer a mutation so great that they totally lose the characteristics of the original cell. The pathologist can recognize that the tumor came from an epithelium, but of which it is impossible to say. This type of malignant cell is called undifferentiated carcinoma or anaplastic carcinoma.
The same organ may have more than one type of carcinoma and more than one type of cancer. For example, of the three most common skin cancers, two are carcinomas (basal cell carcinoma and squamous cell carcinoma) and one is non-carcinoma (melanoma). In lung cancer, the four most common types of cancer are all originated from epithelial cells: small cell lung cancer, squamous cell carcinoma of the lung, lung adenocarcinoma, and carcinoma of large lung cells.
If the cancer arises from an epithelial tissue that contains glands, such as the stomach, colon, pancreas, prostate or breast, the carcinoma is called adenocarcinoma (adeno = belongs to a gland).
In the breast, adenocarcinoma is the most common type of cancer, corresponding to more than 90% of the cases. Breast adenocarcinoma is divided into two groups:
Ductal carcinoma of the breast, when the origin of the cancer are the ducts that carry the milk.
Lobular carcinoma of the breast, when the origin of the cancer are the bulbs, small bags that stores the milk.
The most common carcinomas and adenocarcinomas are the skin, prostate, lung, breast, colon, uterus, liver, kidneys and pancreas.
Carcinoma in situ is the earliest form of cancer when tumor cells are still restricted to the place of its origin, there is no invasion of surrounding structures or spread of disease by blood (no metastasis). To treat carcinoma in situ, it is sufficient to surgically remove the tumor, as all malignant cells will be restricted to this piece of tissue removed.
The various types of carcinomas are very different cancers. In common, only the origin in an epithelial tissue. Only the information of a cancer to be a carcinoma is not sufficient to determine the aggressiveness, the prognosis and the type of ideal treatment.
Some carcinomas are very aggressive, such as carcinoma of the pancreas or carcinomas of the lung; others are slower in progress, such as prostate carcinoma or basal cell carcinoma of the skin.
Each carcinoma has to be assessed individually, taking into account its aggressiveness and the stage at which the tumor is at the time of diagnosis. An in situ carcinoma has an excellent prognosis, whereas the majority of carcinomas diagnosed after metastases already present poor prognosis and short survival.
