[A Case of Pseudopancreatic Cyst Development during Bevacizumab plus Paclitaxel Therapy for Pancreatic Metastasis of Breast Cancer].

A 70s woman with pancreatic metastases of HER2-negative breast cancer was being treated with bevacizumab plus paclitaxel. Tumor markers decreased after treatment initiation. After 8 months of treatment, the patient developed abdominal pain and distention, along with loss of appetite. Contrast-enhanced abdominal CT scan images showed the presence of a large 25 cm pseudopancreatic cyst and disappearance of the pancreatic metastatic lesions. Endoscopic ultrasound-guided cystogastrostomy was performed and an AXIOS stent was placed in the lower part of the gastric body. Subsequently, the cyst disappeared and her abdominal symptoms improved. The patient was able to resume treatment with other drugs and did not experience any recurrence of pancreatitis. Four months later, the AXIOS stent was removed. Bevacizumab plus paclitaxel is reportedly effective against HER2-negative metastatic breast cancer. Bevacizumab is a molecular targeted therapy against vascular endothelial growth factor, and the mechanism of its antitumor effect and complications are different from those of conventional drugs. Paclitaxel has also been reported to cause pancreatitis in rare cases. In this case, the mechanism of response to bevacizumab plus paclitaxel for metastatic pancreatic lesions or the development of drug-induced pancreatitis was considered to be the cause of pseudopancreatic cyst formation.