Problems in the interpretation of apparent ‘radial growth phase’ malignant melanomas that metastasize

Abstract

These cases suggest that, while true RGP melanomas have an excellent prognosis, caution must be exercised in defining a lesion as having no metastatic potential when multiple sections of the primary lesion are unavailable, when the lesion is accompanied by regressive changes, or when there is an associated melanocytic nevus. It is possible that strictly defined RGP melanomas may metastasize in very rare cases. Our observations also suggest that metastatic potential is a function of numerous factors, and may not be evaluable on morphological grounds alone.

Completely regressed primary cutaneous malignant melanoma with nodal and/or visceral metastases: A report of 5 cases and assessment of the literature and diagnostic criteria

“…In particular, thin melanomas (\1 mm) may show focal regression in 7% to 61% of all lesions. 60 Adjacent to unequivocal melanoma, one may observe the wellrecognized features of regression (Fig 7). When observed, regression should always be reported, as it may be evidence of prior deeper invasion.…”

The gene expression signatures of melanoma progression

“…This phase is followed by the development of vertical growth phase, which has been postulated to be the first point at which the tumor gains metastatic capacity. However, metastasis occurs, although with decreased frequency, in patients whose primary melanoma pathology exhibits only a radial growth pattern (3). Previous transcriptome analysis in melanoma defined a cluster of genes expressed in a majority of metastatic melanomas (4); however, this cluster was not related to radial or vertical growth, and precursor nevi (moles) and primary melanomas were not examined.…”

Prognostic Factors in Cutaneous Melanoma

“…Similar results in another large case-control study of thin (<1 mm) metastasizing melanomas have been reported, in which 41 % of metastasizing lesions were in the radial growth phase at the time of original diagnosis [ 57 ]. Two additional instances of metastasizing radial growth phase melanomas were independently described [ 58 ]. Moreover, interobserver concordance in assigning growth phase has not been accurately quantifi ed.…”