What does "in situ" mean when talking about skin cancer?

What does "in situ" mean when talking about skin cancer?

Harry Saperstein, MD, FAAD (Dermatologist, Clinical Assoc. Professor, Medicine, Private Practice and UCLA) gives expert video advice on: Why is the sun harmful to my skin? and more...

"In situ" skin cancers are those skin cancers which are still located only within the epidermis. A squamous cell carcinoma in situ would be those cells that are abnormal; that are just in the outermost layer of the skin and have not reached into the epidermis. The malignant melanoma in situ, as well, means that those cells still remain in the epidermis and have not grown into the dermis. These are what would be called "non-invasive" forms of these skin cancers and because of this, their risk to the patient approaches zero from a mortality standpoint. They still have to be removed because by their nature, it's just a matter of time before their invasiveness does occur and that their aggressiveness is manifested.