Recurrent Gastrointestinal Stromal Tumors in the Imatinib Mesylate Era: Treatment Strategies for an Incurable Disease

BRD4 promotes tumor progression and NF-κB/CCL2-dependent tumor-associated macrophage recruitment in GIST

The most commonly occurring sarcoma of the soft tissue is gastrointestinal stromal tumor (GIST). Treatment and prevention of the disease necessitate an understanding of the molecular mechanisms involved. However, the role of BRD4 in the progression of GIST is still unclear. While it is known there are abundant infiltrating tumor-associated macrophages (TAMs) in the tumor microenvironment, the exact role of these cells has yet to be studied. This work showed an upregulation of BRD4 in GIST that was associated with GIST prognosis. Through gain and loss of function studies, it was found that BRD4 promotes GIST growth and angiogenesis in vitro and in vivo. Mechanistically, BRD4 enhances CCL2 expression by activating the NF-κB signaling pathway. Furthermore, this CCL2 upregulation causes recruitment of macrophages into the tumor leading to tumor growth. A likely mechanism for interactions in the GIST microenvironment has been outlined by this work to show the role and potential use of BRD4 as a treatment target in GIST.

Case report of rhabdomyosarcomatous transformation of a primary gastrointestinal stromal tumor (GIST)

Background

Gastrointestinal stromal tumor (GIST) is the most common primary mesenchymal neoplasm of the gastrointestinal tract. Mutations of KIT and platelet-derived growth factor receptor alpha have been well characterized in GISTs. Patients with KIT mutations are generally sensitive to treatment with tyrosine kinase inhibitors. However, some patients with GIST, while initially sensitive to TKIs, gain resistance in later stages of treatment. Heterologous rhabdomyomsarcomatous dedifferentiation of advanced GISTs after long-term imatinib mesylate (IM) therapy has been reported. In these cases, the underlying molecular mechanism of tumor progression and transformation is unclear.

Case presentation

We report one such patient with rhabdomyosarcomatous dedifferentiation of a GIST without metastatic disease after brief 3-month therapy with IM. The tumor was composed of two distinct phenotypes, a CD117 negative region with rhabdomyosarcomatous differentiation directly adjacent to a CD117 positive classic GIST region. Molecular analysis identified the activating KIT exon 11 mutation in both regions, indicating a common origin for both phenotypes. Additionally, the dedifferentiated component contained two synonymous variants in platelet-derived growth factor receptor alpha and KIT. The increased number of synonymous variants in the rhabdomyosarcomatous region may reflect increased genetic instability of this tumor that may have resulted in the loss of CD117 expression in the dedifferentiated component.

Conclusion

This study adds to the growing consensus that rhabdomyosarcomatous GIST progresses from a common GIST primary tumor. The role of IM in this progression is uncertain; however short duration of IM treatment in this study supports the hypothesis that rhabdomyosarcomatous GIST progression is not a consequence of IM therapy. Furthermore, we provide additional information supporting the observation that CD117 negative rhabdomyosarcomatous transformation maintains the activating KIT variant without KIT expression.

Tumour lysis syndrome: a rare side effect of imatinib therapy for GIST

Tumour lysis syndrome (TLS) is a life-threatening complication wherein massive tumour cell lysis results in severe metabolic abnormalities. TLS generally follows chemotherapy of rapidly proliferating haematological malignancies; spontaneous TLS and TLS from treatment of solid tumours are infrequently reported. We present a rare case of TLS following treatment of a large gastrointestinal stromal tumour (GIST) in a 63- year-old man. Imatinib was started for tumour size reduction prior to surgical intervention and in 5 days the patient developed metabolic derangements consistent with TLS. Imatinib was held and fluids, allopurinol and rasburicase were started. All metabolic abnormalities resolved in 3 days. Imatinib was restarted, and he eventually underwent surgical intervention. This is the second case demonstrating successful reinitiation of imatinib following TLS when treating GIST. We highlight the importance of risk factor assessment and need for pre-emptive therapy to prevent TLS when using tyrosine kinase inhibitor therapy.