Biochemical Pseudoprogression in Pancreatic Cancer During Chemotherapy: A Case Report.

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy, most often diagnosed at an advanced stage, with limited treatment options and poor outcomes. CA 19-9 is the most commonly used biomarker to support the diagnosis and for treatment monitoring of PDAC, but rising levels during treatment usually suggest disease progression. Pseudoprogression, a transient increase in tumor burden or biomarker levels followed by subsequent improvement, has been described in glioblastoma and in cancers treated with immune checkpoint inhibitors (ICIs), but to our knowledge, it has not previously been reported in pancreatic cancer treated with cytotoxic chemotherapy. We describe a 52-year-old man with metastatic PDAC who was treated with FOLFOX due to underlying cardiac comorbidities. Despite rising CA 19-9 levels from 2,344 U/mL at baseline to more than 90,000 U/mL after two months of therapy, the patient experienced clinical improvement, with resolution of abdominal pain, regained appetite, weight recovery, and enhanced performance status. Continued treatment resulted in a subsequent decline and plateau of CA 19-9 levels, consistent with biochemical pseudoprogression. This case represents a unique and previously undocumented phenomenon of pseudoprogression in PDAC under chemotherapy, underscoring the importance of integrating clinical status with biomarker interpretation to avoid premature discontinuation of effective treatment.