Combination of Type I and II tyrosine kinase inhibitors-avapritinib and sunitinib-in refractory gastrointestinal stromal tumor after failure to multi-line therapy: a case report.

Background: Tyrosine kinase inhibitors (TKIs) are currently the main treatment choice for gastrointestinal stromal tumors (GISTs). However, the long-term use of TKIs can lead to drug resistance. There is no study or clinical report of combination therapies of TKIs that have been approved for marketing. Combination pharmacotherapy is a new approach for patients who do not respond to monotherapy. This case provides a reference value for selective combination of TKIs in treating advanced GIST.

Case Description: In this article, we report the case of a 55-year-old female who was diagnosed with duodenal GIST in April 2018 and underwent R0 resection. KIT exon 9 mutation was detected. The patient had disease recurrence with multiple abdominal metastases during imatinib adjuvant therapy after 27 months, and failure to 2nd-line sunitinib treatment after 6 months. She underwent a cytoreductive surgery (R1), and the postoperative mutation analysis suggested KIT exon 9 mutation, with newly found secondary KIT_exon16_p. L783V mutation and other mutations on TP53, POT1, and SETD2, etc. The patient experienced short-term tumor control of standard 3rd-line therapy of regorafenib and the rapid progression of the 4th-line of ripretinib afterwards. Different TKI combination therapies (i.e., ripretinib plus sunitinib, ripretinib plus avapritinib and avapritinib plus sunitinib) were administered to the patient sequentially. Ripretinib plus sunitinib led to stable disease but was discontinued due to intolerable adverse effects. Finally, the patient received a combination regimen of avapritinib plus sunitinib. The patient's tumor showed continuous shrinking in 2 consecutive computed tomography scan evaluations within 4 months with acceptable side effects.

Conclusions: Combined type I and type II TKIs of avapritinib combined with sunitinib therapy achieved tumor regression for a heavily multi-line treated patient. Our case provides a reference for a savage treatment choice in refractory GISTs after failure to all standard treatment.