HER2-positive rectal adenocarcinoma metastatic to the pancreas complicated by obstructive pancreatitis and an infected pseudocyst: a case report.
Hiroumi Akita, Hideaki Miyamoto, Kazuki Kobayashi et al.
✦ AI-curated · Sources linked
Case in brief
A man in his 60s presented with cerebellar masses; PET-CT also showed hypermetabolic lesions in the rectum and pancreas. Testing identified HER2-positive, RAS/BRAF wild-type rectal adenocarcinoma. The pancreatic lesion caused obstructive pancreatitis and an infected pseudocyst. EUS-guided tissue acquisition showed metastatic colorectal adenocarcinoma, distinguishing it from a primary pancreatic cancer. After antibiotics controlled the infection, cytotoxic chemotherapy was considered high risk, so trastuzumab plus pertuzumab was started. After four cycles, tumor marker levels fell and imaging showed regression of the pancreatic metastasis and improvement of the pseudocyst.
What made this case unusual
The pancreatic metastasis was complicated by both obstructive pancreatitis and an infected pseudocyst, creating an infectious complication that made cytotoxic chemotherapy high risk.
Diagnostic / clinical pearl
Imaging alone may not distinguish pancreatic metastasis from a primary pancreatic cancer. EUS-guided tissue acquisition can establish tumor origin, which is essential when treatment depends on the primary cancer type.
Why it matters
In this case, dual HER2-targeted therapy was followed by tumor marker decline and radiologic improvement when infectious complications made cytotoxic chemotherapy high risk.