A Novel Fusion in Gastrointestinal Stromal Tumor Guides Adjuvant Treatment Decision-Making During Pregnancy.

Gastrointestinal stromal tumors (GISTs) are rare in pregnancy, with only 11 reported cases. Adjuvant imatinib therapy, which targets the most common driver mutations in GIST ( and , is recommended for patients with high-risk GIST, but it has known teratogenicity in the first trimester. A 34-year-old G3P2 woman underwent exploratory laparotomy at 16 weeks' gestation for a presumed adnexal mass. Surgical findings included normal adnexa and a 14-cm solid small bowel mass. The mass was resected en bloc with a segment of jejunum followed by a primary anastomosis. Histopathology and genomic analyses demonstrated a GIST with high-risk features but lack of mutations and identified the presence of a previously unreported, pathogenic gene fusion. Given her tumor profile, adjuvant therapy with imatinib was not recommended. GIST is rare in pregnancy, but can masquerade as an adnexal mass in women of childbearing age. Because neoadjuvant/adjuvant imatinib has risks of teratogenicity, tumor molecular profiling is critical as we identified a previously unreported gene fusion of with that is predicted to be imatinib-resistant. In this case, testing provided the rationale for not offering adjuvant imatinib to avoid unnecessary toxicity to the patient and fetus.