Nodular melanoma has no known precursor. It is a small black, or if amelanotic, pink nodule that simply enlarges. The absence of a precursor lesion means that nodular melanomas tend to be diagnosed later than superficial spreading melanomas. This lateness means that they are thicker at the time of diagnosis, on average, and tend to have a worse prognosis because of that.
Amelanotic melanoma, a pink to purple-red nodule, is particularly likely to be diagnosed late because neither physicians nor the public expect a pink lesion to be a melanoma. A rapidly growing pink nodule can be amelanotic melanoma or squamous carcinoma, among a broad differential diagnosis.
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