Pathogenesis.

• UV radiation leads to formation of pyrimidine dimers in DNA, which is a type of DNA damage that is responsible for carcinogenicity.


#### **Table 8.**

*Occupational cancers.*


#### Ionizing radiation**:**

Electromagnetic (x-rays, γ-rays) and particulate (α particles, β particles, protons, neutrons) radiations are all carcinogenic.

*Neoplasia DOI: http://dx.doi.org/10.5772/intechopen.109512*

#### **Figure 2.**

*Multistep theory of chemical carcinogenesis.*

Cancers produced:

Medical or occupational exposure, for example., leukemia and skin cancers. Nuclear plant accidents: Risk of lung cancers.

Atomic bomb explosion: Survivors of atomic bomb explosion (dropped on Hiroshima and Nagasaki) -› increased incidence of leukemia -> mainly acute and chronic myelogenous leukemia after about seven years.

Subsequently, increased mortality due to solid tumors (e.g., breast, colon, thyroid, and lung).

Therapeutic radiation:


Mechanism: Hydroxyl free radical injury to DNA.

Tissues that are relatively resistant to radiation-induced neoplasia: Skin, bone, and the gastrointestinal tract.

UV rays cause skin cancer:

1.Squamous cell carcinoma.

2.Basal cell carcinoma.

3.Malignant melanoma.

Lymphoid tissue: most sensitive to radiation.

Bone: least sensitive to radiation.

UV radiation: induces formation of pyridine dimers in DNA leading to mutations. Acute leukemia: most frequent malignant tumor caused by radiation.

Total body radiation: lymphopenia is the first hematological feature.

Xeroderma pigmentosum is caused due to abnormalities in nucleotide excision repair.

Ionizing radiation: Damages DNA.

Ionizing radiation causes genetic damage which cannot be repaired by nucleotide excision repair.

Neoplasm associated with therapeutic radiation.

1.Papillary carcinoma of thyroid.

2.Angiosarcoma of liver [21, 22].
