Measuring the horizontal and vertical growth rates of superficial spreading melanoma: a pilot study with sequential digital dermoscopy.

Background: Some authors have hypothesized that the initial kinetics of the primary melanoma (MM) growth could reflect its biologic aggressiveness. The aim of this study was to pilot a measure of the horizontal vs. vertical growth of superficial spreading melanomas (SSM).
Methods: The dermoscopic images of twenty-three consecutive MMs (17 SSMs and 6 MMs in situ), excised after digital sequential dermoscopy, were reviewed. We built up two indexes: 1) dROG (digital Rate of Growth) defined as Breslow thickness/(t1-tR), where t1 was the reported time of the first dermoscopic image acquisition and tR was the reported time of the acquisition before the lesion excision; 2) lHGR (linear Horizontal Growth Rate) took into account the greater axis of the lesion at two time points, at the time (t1) of the first image acquisition (D1) and before (tR) lesion excision (DR). The index was computed as (DR-D1)/(t1-tR). We built up the Composite Rate of Growth index (cROG) calculated as dROG/lHRG. If the value of cROG is <1 the superficial growth is prevalent on the vertical growth, and if the value is >1 the vertical growth is prevalent on the superficial growth.
Results: In 82.6% of lesions the horizontal growth was prevalent on the vertical growth, and in 17.4% of cases the vertical growth was equal or prevalent on the superficial growth.
Conclusions: A small proportion of SSMs with a slow horizontal growth could have a precocious vertical growth. Other larger studies are needed to confirm this observation.