IMMUNITY AND CANCER

Incidence

Mortality due to different types of cancers ranks among the top three causes of death, usually alongside cardiovascular diseases.

The incidence varies by gender, with a higher incidence of lung, prostate, and colorectal cancers in men; While there is a higher incidence of breast, colorectal, and uterine cancers in women.

Lately, several therapeutic strategies, such as monoclonal antibodies, in addition to radiotherapy and chemotherapy, have been approved, significantly improving survival rates. Nevertheless, there are still cancers with very high mortality, such as pancreatic cancer, which has an almost 100% mortality rate, as it is among the least treatable.

Neoplasia

• Literally means "new growth," therefore, it is the development of new tissue.
• It can be categorized as neoplasia when this developed mass of tissue is abnormal (cells not fully differentiated, and they do not follow the structure and architecture that would be expected for the type of tissue/organ where it is developing).
• Excessive, uncoordinated growth compared to normal tissue.
• Growth is continuous, even if the inducing stimulus is interrupted (if known).

Tumor

• Increase in volume in a tissue, can be caused by edema or hemorrhage.
• A tumor can be an immune activation (inflammation), where the permeability of blood vessels increases, and fluid and cells can accumulate.
• Medically, it also applies to neoplastic masses.

Benign Neoplasia

• Slow and uniform growth.
• Usually well-defined and easily removable (depending on the accessibility of the anatomical region).
• May cease to grow due to different factors. It does not have to be in constant evolution and can even be reduced.

To designate them, most are named by adding the suffix -OMA to the type of cell from which the neoplasia originates.

Malignant Neoplasia (Cancer)

• Invades and destroys adjacent structures. Great invasive capacity.
• Ability to spread to distant tissues through hematogenous dissemination if they reach blood vessels (Metastasis: initiation of another cancerous focus in a distant region).
• Contrary to common belief that cancer cells are completely undifferentiated, cells can have a certain degree of differentiation that varies according to the type of cancer. From well-differentiated cells to completely undifferentiated ones.

To designate them, most are named by adding the suffix -SARCOMA (if the cells are of mesenchymal origin) or -CARCINOMA (if the cells are of epithelial origin) to the type of cell from which the neoplasia originates.

Carcinogens

In addition to having a genetic component, cancers also have exogenous factors that cause alterations in cell replication or damage to cellular DNA, potentially triggering the appearance of the tumor.

These can be:

The development of cancer due to exposure to carcinogens depends on many factors, such as the route, duration, and intensity of exposure, in addition to personal genetic background. Various agencies have conducted classifications of carcinogens.

According to the International Agency for Research on Cancer (IARC), which is part of the WHO, we have the following classification:

• GROUP 1 : Carcinogenic to humans.
• GROUP 2A : Probably carcinogenic to humans.
• GROUP 2B : Possibly carcinogenic to humans.
• GROUP 3 : Not classified as carcinogenic to humans.
• GROUP 4 : Probably not carcinogenic to humans.

This classification is based on:

• Agents : Epidemiological and/or experimental evidence (in vitro / in vivo).
• Doses : Dose-dependent risk, taking into account susceptible populations (children, elderly, pregnant individuals,...).
• Exposure : Time, duration, and route of exposure.

Transformation

This malignant neoplasia with the ability to invade tissues is mainly due to a failure (alteration) in the regulatory controls that guide the proliferation, differentiation, and survival of cells.

One of the most characterized alterations is in the proto-oncogenes. Proto-oncogenes are genes whose activation can promote controlled cell growth and division (positive regulators of growth). They are regulated and are particularly active in early stages of embryonic development, with deactivation as the organism stops growing.

An anomalous version of these genes can lead to overexpression, promoting uncontrolled growth that often escapes cellular control. A proto-oncogene and an oncogene differ in the version of this gene, with oncogenes being the anomalous version of proto-oncogenes.

Many proto-oncogenes express signal transduction molecules related to cellular activation pathways, transcription factors that regulate gene expression, membrane receptors for growth factors, or cyclins that regulate the cell cycle.

There is not always a direct relationship between the type of cancer and the activated proto-oncogene; that is, the same proto-oncogene can give rise to different types of cancer depending on the part of the body where it is altered.

Another important factor that contributes to carcinogenesis is alterations in tumor suppressor genes. Tumor suppressor genes encode proteins that regulate cell growth by suppressing proliferation (negative regulators of growth).

Therefore, there is typically a balance between the activity of proto-oncogenes and tumor suppressor genes, allowing for tissue population renewal through this balance.

Balance

When there is an imbalance, cancers can emerge. This can occur due to the activation of oncogenes or alterations in tumor suppressor genes.

Imbalance