What is the difference in melanoma and invasive melanoma?

Spread of cancer. Melanoma in situ is the term used to describe when the skin cancer only involves the surface (epidermis) of the skin and has not spread to any other tissues in the body; there is a 99.9% five year survival rate. Invasive melanoma indicates that the cancer has spread below the surface into the dermis of the skin. Metastatic melanoma indicates spread of the cancer to other areas in the body.
Invasive melanoma. During vertical growth phase (VGP) the tumor is usually > 1 mm thick & may move into the tissues around it (or enter lymphahic or circulatory system.
How far it's gotten. Malignant melanomas start in the epidermis, the outer layer of your skin. If the pathologist sees even a single cell invading the lower layer (the dermis), the melanoma is considered invasive and there is therefore the possibility that it has spread further and your life is in danger. If a non-invasive melanoma is removed, it can be considered cured.
Not much. Melanoma is a type of skin cancer, more common in white people who were exposed to sun without UV protection. Invasive melanoma is called when the cancer cells reached the level of the papillary dermis and deeper (layers of the skin). Melanoma is called when the cancer cells are above the papillary dermis.