Keratoacanthomas and Spitz Tumors: Are They Both ‘Self-Limiting’ Variants of Malignant Cutaneous Neoplasms?

Abstract

The first striking similarity between KA and ST is represented by their evolution, which is characterized by 3 phases, namely growth, stabilization and involution, as shown in figure 1 [1, 7, 8] . The first phase is characterized by a rapid increase in size within a few weeks or months. Such a high proliferation rate is extremely unusual for any kind of benign melanocytic skin tumor and almost exclusively observed in biologically aggressive tumors such as nodular melanoma [9] . Thus, the growth attitude of KA and ST is in favor of the malignant nature of these cutaneous neoplasms. In contrast, the subsequent stabilization and final involution deviate clearly from the expected course of a malignant tumor, and move KA and ST closer to the spectrum of benign skin neoplasms. Involution of KA is a well-recognized phenomenon, but it has been only recently described in ST ( fig. 2 ). In our original report, we observed the progressive disappearance of 2 cases of pigmented ST in children during a follow-up period of 6 months and 3 years, respectively [8] . Since then, further cases of involuting ST in children have been published [10–12] . Although these preliminary data do not allow estimating the proportion of ST undergoing involution, From a purely morphological point of view, keratoacanthoma (KA) is a form of squamous cell carcinoma (SCC) since it reveals similar clinical and histopathological-cytological features as SCC [1] . However, it is well recognized that the morphological similarity between KA and SCC contrasts with their different biological attitudes. While SCC is a biologically malignant tumor characterized by the potential to progress, destroy tissue, metastasize and cause death, KA consistently undergoes spontaneous involution [1, 2] . For this reason, KA is widely accepted to be a self-limiting or ‘biologically benign’ variant of SCC. Such a disparity between ‘malignant’ morphology and ‘benign’ biology exists also within the spectrum of melanocytic neoplasms, as in the case of Spitz tumors (ST). This group of melanocytic proliferations can be morphologically indistinguishable from melanoma but follow typically a benign clinical course [3–6] . Consequently, it is legitimate to question whether the concept of the existence of a ‘self-limiting’ variant can be extended to the spectrum of melanocytic ‘spitzoid’ tumors. Indeed, common features between KA and ST do exist supporting such a concept, which we will discuss further in detail. Published online: April 16, 2009