What is the most common type of skin cancer, which results in the formation of a nodule with a central "crater" that ulcerates?

Basal cell carcinoma. (BCC).

This occurs when exposure of the skin to ultraviolet rays damaged the DNA of the exposed area by forming thymine dimer. Besides the UV exposure may also suppress the hormone surveillance mechanism; enabling the tumour cells in the basal cells to escape the immune surveillance radar, leading to cancer growth.

Thymine dimers are formed when two thymine molecules formed a complex by co-valent bond on the same single strand of DNA. They lead to mutation when their complex is replicated as a base, leading to frameshift mutation.

Exposure to radiation especially during childhood stage, having light skin, indoor tanning (which may prompt uncontrolled growth in the basal Cells) are among other causative factors.

Its appearances vary in structure, and skin pigmentation. it does not in most cases extend beyond the local areas. However if not given proper treatment attention it may disfigure the skin, causing massive damages by growing deep into the dermis to reach the blood through the subcutaneous tissue to the bone. It may also metastasize, (spread) causing cancerous growth in other parts of the body.

Treatment involve surgical removal.

Basal cell carcinoma

Explanation:

Basal cell carcinoma is a common type of skin cancer, it appears as raised part in the skin that is painless with shiny blood vessel running over it or may be ulcerative