How does a pathologist identify nodular melanoma as opposed to superficial or other types under a microscope? does it look different?

Very much so: It's the distribution of the abnormal cells in relationship to the remaining normal structures. I trained under one of the premiere surgical pathologists of his generation and even then, he would never sign out a melanoma without a second pathologist.

Difficult: This is probably the most difficult diagnosis for a pathologist. So much so, that many dermatopathologists are now making this diagnosis. The cells do look similar under a microscope but many of the characteristics are based on clinical appearance, pattern of spread, and anatomic location. While other tumors do have distinct "looks" to them, Melanoma is much more complicated.

Different: Different cancers look differnty to the trained eye

Not flat: It is deep (vertical) more than it is wide (horizontal). The clinical appearance is a RAISED lesion. Most melanomas are flat (superficial, in situ) and are spreading outward. A nodular one is spreading downward deeper into the skin.