KIT and Kaposi's sarcoma: Misinterpretation of immunostaining for CD117 however remains the main reason for diagnostic error, both with other CD117-positive tumours such as Kaposi sarcoma [7] and with nonspecific weak background staining for this marker (and occasional cytoplasmic positivity in myofibroblastic lesions) [8] which is often mistaken for diffuse positivity.