A case report of a collision tumor composed of pancreatic ductal adenocarcinoma and peri-pancreatic mucosa-associated lymphoid tissue lymphoma oleh Ryuji Hirai, Ken-ichi Omae, Mitsuko Yodoya, Syunji Fujie, Masayoshi Fujii, Kazuma Iwata, Kentaro Imanishi, Eisuke Kurihara, Kazuhiro Yoshida, Masaru Jida, Kazuyasu Kobayashi, Yoshiaki Kanaya, Syuichiro Maruyama