Figure 2. Radiographic Responses to Imatinib Mesylate.

MRI indicates magnetic resonance imaging; PET, positron emission tomography. MRI and PET scans from a representative patient with vulvovaginal mucosal melanoma harboring both an exon 11 L576P mutation and amplification of KIT are shown at baseline (yellow arrows, A and C) and after 6 weeks of therapy with imatinib mesylate (yellow arrows, B and D). The arrowhead in A indicates a heterogeneous multilobulated mass distending the entire vagina and extending inferiorly to the introitus. This lesion demonstrates intense fluorodeoxyglucose uptake on PET imaging (arrowhead in C). After 6 weeks of therapy with imatinib mesylate, there was significant shrinkage in the size of this mass with interval resolution of hypermetabolic activity (arrowheads in B and D indicate baseline locations of tumor). This patient ultimately achieved a complete radiographic response to therapy at her week 12 scan. Baseline and posttreatment PET images of a second representative patient with an acral melanoma harboring an exon 11 576P mutation and amplification are shown in E and F. This patient ultimately achieved a complete radiographic and pathological response to therapy at his week 12 scan.