The three forms of skin cancer are defined by the types of cells from which they originate

Basal cell carcinoma

This skin cancer occurs in the basal cells of the skin which are in the deepest part of the skin's outer layer. Rarallyspreads to other regions of the body but the treatment should still be as quickly as possible. 
This cancer is caused by too much sun exposure.

Squamous cell carcinoma

This type of cancer is not limited to the skin and It can happen in any tissues that contain squamous cells.This cancer is more likely to spread than the basal cell carcinoma.It's caused by too much sun exposure.

Melanoma

Melanoma is the rarest out of these forms of skin cancer, but it is the most dangerous and can be fatal.

It's a malignant tumor that originates in melanocytes which are the cells that produce melanin (the pigment that gives colors to the skin, hair and eyes).

A. mitochondrion b. nucleus