Multiple primary tumors patient developed microsatellite stable gastric cancer after cadonilimab treatment for liver cancer: A case report.

Background: Multiple primary malignant tumors refer to the occurrence of two or more primary malignant tumors in the same organ or multiple organs or tissues at the same time or successively in the same patient, and can occur anywhere in the body. The treatment guidelines for patients with multiple primary malignant tumors are currently controversial.

Case summary: A 51-year-old male patient with liver cancer and portal hypertension received 42 months of co-treatment with atezolizumab and bevacizumab. After that, the disease was rated stable disease. The patient was then diagnosed with gastric cancer. Since the patient was not sensitive to anti-programmed death ligand 1 immunosuppressive agents, a co-treatment with oxaliplatin, tegafur, apatinib, and cadonilimab was selected after multidisciplinary consultation and the patient's agreement. After four cycles of treatment, partial response and stable disease were observed in gastric and liver cancers, respectively. Surgical treatment was performed considering the high-risk factors of gastrointestinal bleeding in patients with gastroesophageal varices. Postoperative pathology showed that the Tumor Regression Grade was 1. Moreover, the genetic testing of postoperative tumor specimens indicated negative programmed death ligand 1 and microsatellite stability. In addition, the latest follow-up indicated an 8 and 40-month progression-free survival in gastric and liver cancer patients, respectively. Currently, the patient is receiving postoperative immunotherapy with cadonilimab.

Conclusion: Cadonilimab not only treats microsatellite stability gastric cancer patients but can also be used for liver cancer treatment.