Metastasis of pancreatic cancer within primary colon cancer by overtaking the stromal microenvironment.

: We report a unique case of a 74-old man, who presented with double cancers, showing metastasis of pancreatic cancer to colon cancer. Histopathological examination after surgery revealed that the patient had ascending colon cancer, which metastasized to the liver (pT4N0M1), as well as pancreatic cancer (pT2N1M1) that metastasized to the most invasive portion of the colon cancer, namely the serosal to subserosal layers. Although the mechanisms for this scenario have yet to be elucidated, we speculate that the metastatic pancreatic carcinoma overtook the stromal microenvironment of the colon cancer. Namely, the cancer microenvironment enriched by cancer-associated fibroblasts, which supported the colon cancer, might be suitable for the invasion and engraftment by pancreatic carcinoma. The similarity of histological appearance might make it difficult to distinguish metastatic pancreatic carcinoma within colon cancer. Furthermore, the metastasis of pancreatic carcinoma in colon carcinoma might be more common, despite it not having been previously reported.