In contrast, thereis a subset of lesions classified as PEComas but harbor TFE3 gene fusions.Distinctive features of TFE3-associated PEComas include a tendency to occurat a younger age, no association with TSC, minimal immunoreactivity for actin or desminmarkers, predominant epithelioid cytology, and strong TFE3 immunoreactivity.7TFE3-associated PEComas are mutually exclusive to those associated with TSC.5 It has been suggested that PEComas that express TFE3immunoreactivity but do not involve the TSC2 gene may be biologicallydistinctive from conventional PEComas. The gene discussed is TFE3; the disease is tuberous sclerosis.