Dedifferentiated gastrointestinal stromal tumour with features mimicking malignant PEComa/alveolar soft part sarcoma: An unusual type of morphological transformation following imatinib treatment

• Main Authors: Kankanamage Malinda Amesh Karasinghe (Author), Kesavan Sittampalam (Author)
• Format: Book
• Published: Elsevier, 2021-03-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 2214-3300; 10.1016/j.ehpc.2020.200457
• Keywords: GIST dedifferentiation; Malignant PEComa; Alveolar soft part sarcoma; Imatinib treatment; Pathology; RB1-214
• Source: Human Pathology: Case Reports, Vol 23, Iss , Pp 200457- (2021)

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. Dedifferentiation is a rare phenomenon in GISTs, most often following long-term Imatinib therapy and less frequently in de-novo fashion. According to the literature, the process of dedifferentiation is likely associated with genetic instability, rather than a result of acquisition of novel mutations in the common driver oncogenes. However, the exact underlying molecular basis of dedifferentiation is not well-established. Dedifferentiated GISTs show anaplastic features with loss of immunoreactivity for CD117 and DOG1. In this report, we present a rare and unique case of dedifferentiated metastatic GIST with a very unusual malignant PEComa/alveolar soft part sarcoma-like morphology. The molecular findings of our case also support the concept that dedifferentiation of GIST is independent of acquisition of additional novel mutations in the common driver oncogenes.