A kinetic model for progression of a population of cutaneous melanomas through categories defined by the range of Breslow thickness, with melanomas in situ (MIS) in category 0, and melanomas with Breslow thickness > or =2 mm in category 3, is described. The model assumes that all melanomas start out in category 0; this category is further subdivided into indolent and progressing melanomas. Steady-state solutions for the distributions of excised melanomas were found. Depending on the proportion of indolent MIS, these solutions predict very different distributions of excised melanomas and melanoma mortality, when either frequency of examinations by physicians or sensitivity to melanoma is changed. Although it is not currently possible to differentiate between indolent and progressing MIS either clinically or histologically, solutions of this kinetic model can be used to determine the proportion of such indolent lesions in a population-based study. The steady-state solutions of the kinetic model can be used to analyze melanoma progression in any stable patient population, in which the total number of melanomas detected per year is either stable or varies slowly. As an example, melanoma progression is analyzed using the American Cancer Society estimates of melanoma incidence and mortality. For a fixed incidence rate, melanoma mortality and melanoma treatment cost in the USA could be significantly reduced by increasing the biopsy sensitivity of physicians to in-situ and thin-invasive melanomas.
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