Descending duodenal adenocarcinoma treated with pembrolizumab resulting in complete clinical response: A case report and literature review

Abstract

BACKGROUND

Descending duodenal adenocarcinoma (DDA) is a rare malignancy of the digestive system, typically characterized by microsatellite instability-high (MSI-H). Pembrolizumab is a monoclonal antibody that has been approved for the treatment of MSI-H solid tumors in China.

CASE SUMMARY

We present the case of a 55-year-old female patient diagnosed with DDA. Biopsy findings indicated MSI-H status with high expression of programmed cell death-ligand 1 (PD-L1). The patient was unable to undergo immediate surgery due to multiple metastatic lymph nodes in the retroperitoneum. After one cycle of the SOX (S-1 + oxaliplatin) chemotherapy regimen, the patient’s performance status significantly declined, and she experienced active gastrointestinal bleeding. Following active communication with the patient's family, pembrolizumab treatment was initiated. After two cycles of treatment, the disease was assessed as a partial response. A positron emission tomography/computed tomography scan performed after two years of treatment indicated a clinical complete response (CCR). The patient maintained this CCR for four years. She has now discontinued pembrolizumab for over one year, and no disease recurrence has been observed during re-examination.

CONCLUSION

Patients with MSI-H DDA exhibiting high PD-L1 expression who are treated with pembrolizumab can achieve sustained CCR.

Keywords: Duodenal malignancy; Microsatellite instability-high; High expression of programmed cell death-ligand 1; Pembrolizumab; Complete clinical response; Case report

Core Tip: Descending duodenal adenocarcinoma (DDA) is a rare malignancy of the digestive system. We treated a patient with DDA characterized by microsatellite instability-high (MSI-H) and high programmed cell death-ligand 1 expression, customizing the treatment regimen for individualized pembrolizumab therapy based on our clinical experience and disease assessment. The patient achieved long-term clinical remission with satisfactory results. This case underscores the advantages of individualized therapy and confirms that patients with mismatch-repair deficiency/MSI-H can derive significant benefits from pembrolizumab.