Management of HER2-positive and microsatellite instability-high advanced gastric cancer: a case report
Taichi Tamura1, Yusuke Kanemasa1, Shohei Nakamura1
1Department of Medical Oncology, Tokyo Metropolitan Cancer and Infectious Diseases Center, Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo, 113-8677 Japan.
Abstract:
Chemotherapy for advanced gastric cancer has progressed significantly in the past few decades. Biomarker-specific drugs, including anti-human epidermal growth factor receptor 2 (HER2) drugs for HER2-positive patients and immune checkpoint inhibitors for those with microsatellite instability-high (MSI-H), have become common. However, patients who are positive for HER2 and have MSI-H are extremely rare, and there are no established treatments for these patients. We present the case of a 75-year-old, male patient with gastric cancer with lymph node metastases and liver infiltration. Biomarker analysis revealed HER2 3 + , loss of MLH1, and MSI-H. After three cycles of S-1, oxaliplatin, and trastuzumab, the primary tumor and metastases shrank markedly. He subsequently underwent gastrectomy and hepatectomy as conversion surgery, achieving a pathologically complete response. He has been recurrence-free for seven months postoperatively. The present case demonstrated the efficacy of trastuzumab-containing chemotherapy followed by conversion surgery in a patient with HER2-positive, MSI-H, advanced gastric cancer.
Insights
Treatment for advanced gastric cancer in a rare HER2-positive, microsatellite instability-high (MSI-H) patient involved trastuzumab chemotherapy and conversion surgery. This approach led to a complete response and recurrence-free survival.
Area of Science:
- Oncology
- Gastrointestinal Oncology
- Biomarker-Driven Therapy
Background:
- Advanced gastric cancer treatment has advanced with biomarker-specific therapies.
- Human epidermal growth factor receptor 2 (HER2)-positive and microsatellite instability-high (MSI-H) co-occurrence is rare in gastric cancer.
- Established treatment protocols for this rare patient subgroup are lacking.
Purpose of the Study:
- To report a successful treatment strategy for an advanced gastric cancer patient with rare HER2-positive and MSI-H biomarkers.
- To highlight the efficacy of a combination chemotherapy regimen followed by conversion surgery.
Main Methods:
- A 75-year-old male patient with advanced gastric cancer, liver metastases, and HER2 3+ and MSI-H status was treated.
- The patient received three cycles of S-1, oxaliplatin, and trastuzumab chemotherapy.
- Conversion surgery (gastrectomy and hepatectomy) was performed after neoadjuvant chemotherapy.
Main Results:
- Neoadjuvant chemotherapy resulted in significant shrinkage of the primary tumor and liver metastases.
- The patient achieved a pathologically complete response after conversion surgery.
- The patient remained recurrence-free for seven months postoperatively.
Conclusions:
- Trastuzumab-containing chemotherapy followed by conversion surgery is an effective strategy for HER2-positive, MSI-H advanced gastric cancer.
- This case demonstrates a viable treatment option for a rare and challenging patient population.
- Biomarker-guided therapy combined with surgical intervention can achieve favorable outcomes in advanced gastric cancer.
