diagnostics Case Report A Pancreatic Inflammatory Myofibroblastic Tumor with Spontaneous Remission: A Case Report with a Literature Review Hiroyuki Matsubayashi 1, * , Katsuhiko Uesaka 2 , Keiko Sasaki 3 , Seitaro Shimada 1 , Kazunori Takada 1 , Hirotoshi Ishiwatari 1 and Hiroyuki Ono 1 1 Division of Endoscopy, Shizuoka Cancer Center, Shizuoka 411-8777, Japan; s.shimada@scchr.jp (S.S.); ka.takada@scchr.jp (K.T.);h.ishiwatari@scchr.jp (H.I.); h.ono@scchr.jp (H.O.) 2 Division of Hepato-pancreaticobiliary Surgery, Shizuoka Cancer Center, Shizuoka 411-8777, Japan; k.uesaka@scchr.jp 3 Division of Pathology, Shizuoka Cancer Center, Shizuoka 411-8777, Japan; k.sasaki@scchr.jp * Correspondence: h.matsubayashi@scchr.jp; Tel.: +81-55-989-5222; Fax: +81-55-989-5692 Received: 25 September 2019; Accepted: 15 October 2019; Published: 17 October 2019   Abstract: The inflammatory myofibroblastic tumor (IMT) is a rare tumor that can develop in any systemic organ. Its features are generally benign, but it often resembles malignancies and is treated surgically. Our patient was an 82-year-old female complaining of abdominal discomfort. Computed tomography demonstrated a 5 cm, ill-enhanced mass at the pancreas head. Upper gastrointestinal endoscopy revealed a duodenal submucosal tumor with apical erosion. Endoscopic ultrasonography (EUS) demonstrated a heterogeneous, low-echoic pancreas mass without clear margins. Fine-needle aspiration biopsy (FNAB) demonstrated spindle myofibroblastic tissues with lymphoplasmacyte and eosinophil infiltration, confirming an IMT diagnosis. Surprisingly, the tumor spontaneously regressed in one month without medication. Histological diagnosis using EUS-FNAB is essential for the rare pancreatic solid tumor like IMT. Keywords: pancreas; inflammatory myofibroblastic tumor; spontaneous regression; diagnosis 1. Introduction The inflammatory myofibroblastic tumor (IMT) is a rare tumorous lesion that can develop in any systemic organ. It has a relatively young onset (mainly in newborns to young adults) and consists histologically of proliferative myofibroblastic tissues with heavy infiltration of inflammatory cells, mainly lymphocytes and plasma cells [1]. It often shows benign biological behaviors, but it is sometimes accompanied by somatic mutations in clinically important genes [2–5] that can cause metastasis and/or recurrence [2,5]. The differential diagnosis from malignancies is therefore difficult, especially in high-aged cases, and most IMTs are surgically resected before finally being diagnosed [2,5–26]. Anti-inflammatory agents, such as corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDS), are effective for some IMTs [27,28], and a small proportion of IMTs regress spontaneously [27–38]. To date, several cases of pancreatic IMTs have been reported [6–26], but histologically proven cases (proven for myofibroblastic component) with spontaneous remission have hardly been reported. 2. Case Presentation An 82-year-old Japanese female was referred to our hospital after a month of complaints of upper abdominal discomfort. First, she visited the nearest hospital and underwent upper gastrointestinal endoscopy that pointed multiple erosions and an extrinsic compression at the posterior pylorus. Diagnostics 2019, 9, 150; doi:10.3390/diagnostics9040150 www.mdpi.com/journal/diagnostics