Guitart et al,1 in their study of histological characteristics of metastasizing thin melanomas, found 10 cases of nontumorigenic (radial growth phase) melanomas associated with metastasis, thus casting doubt on the clinical relevance of the growth phase theory. We could not discern how many of those 10 cases were associated with regression, which, if present, might have helped to explain the associated metastasis on the basis that the primary tumor may have been in vertical growth phase before the onset of regression. An alternative explanation, however, is that the patients may have had other, thicker primary melanomas that were responsible for the metastases.
Peter J. Heenan, John M. Taran. Metastasizing Thin Melanoma or Multiple Primary Melanomas?. Arch Dermatol. 2003;139(3):388. doi:10.1001/archderm.139.3.388-a