"In Situ" describes the depth or stage of the skin cancer Melanoma. The term "In situ" literally means "in the original position or place". This means the Melanoma cancer is in the outermost layer of your skin and the cancer has not spread to further layers of your skin. This would be considered stage 0 of melanoma cancer, and has a curing rate of about 95%, as long as you pursue treatment. You .