Answer C) Hypodermis
Tumor thickness is one of the most important prognostic factors for malignant melanoma.
The hypodermis (subcutis) is the deepest layer of the skin, and melanoma mortality is directly correlated with tumor thickness.
Due to variability in the thickness of skin compartments among different individuals, tumor thickness does not always correspond with skin layer invasion.
However, in this patient it is likely that a tumor extending into the hypodermis is thicker than a tumor in a more superficial layer.
Breslow depth is the most important prognostic factor used for melanoma staging and to determine the safety margin of a full-thickness incision.