title: Not all mixed-type intraductal papillary mucinous neoplasms behave like main-duct lesions: implications of minimal involvement of the main pancreatic duct.
abstract: BACKGROUND
  The malignant potential of intraductal mucinous neoplasm of the pancreas (IPMN) is associated closely with main pancreatic duct (MPD) involvement. Because mixed-type IPMN is thought to have the same malignant potential as that of main-duct (MD)-IPMN, resection is recommended; however, the biological nature of mixed-type IPMN with only minimal involvement of MPD (min-mix-IPMN) may be different.
  
  
  METHODS
  A prospective database of 404 resected IPMNs was re-reviewed to subclassify mixed-type IPMNs. We defined min-mix-IPMN as absence of gross abnormalities (except for dilatation) of MPD and noncircumferential microscopic involvement of MPD limited to few sections.
  
  
  RESULTS
  We identified 46 min-mix-IPMNs, 163 IPMNs with extensive involvement of MPD (ex-mix-IPMN), 175 branch-duct (BD)-IPMNs, and 20 MD-IPMNs. The majority of min-mix-IPMNs were found incidentally and increased cyst size on surveillance was the leading operative indication. The median diameter of MPD was 2 mm in min-mix-IPMN versus 9 mm in ex-mix-IPMN (P < .0001), and cysts ≥10 mm were present in 62% of ex-mix-IPMNs versus 93% of min-mix-IPMNs (P < .0001). Most importantly, the vast majority of min-mix-IPMNs exhibited gastric-type epithelium, similar to BD-IPMNs, whereas intestinal-type epithelium was present in half of ex-mix-IPMNs, similar to MD-IPMNs. The prevalence of high-grade lesions was less in min-mix-IPMN than ex-mix-IPMN (P < .0001). These differences were reflected in better disease-specific outcomes of min-mix-IPMN compared with ex-mix-IPMN (P = .046).
  
  
  CONCLUSIONS
  Min-mix-IPMN often presents with no MPD dilation and is an incidental finding by microscopic examination. min-mix-IPMN shares the pathologic features and less aggressive biology with BD-IPMN. We propose that min-mix-IPMN be categorized differently than ex-mix-IPMN.
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Klaus
authors: K
authors: Sahora
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Carlos
authors: C
authors: Fernández-del Castillo
authors: Department of Pathology, Massachusetts General Hospital, Boston, MA.
authors: Fei
authors: F
authors: Dong
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Giovanni
authors: G
authors: Marchegiani
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Sarah P
authors: SP
authors: Thayer
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Cristina R
authors: CR
authors: Ferrone
authors: Department of Radiology, Massachusetts General Hospital, Boston, MA; Department of Radiology, Harvard Medical School, Boston, MA.
authors: Dushyant V
authors: DV
authors: Sahani
authors: Division of Gastroenterology, Massachusetts General Hospital, Boston, MA; Department of Internal Medicine, Harvard Medical School, Boston, MA.
authors: William R
authors: WR
authors: Brugge
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Andrew L
authors: AL
authors: Warshaw
authors: Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
authors: Keith D
authors: KD
authors: Lillemoe
authors: Department of Pathology, Massachusetts General Hospital, Boston, MA; Department of Pathology, Harvard Medical School, Boston, MA. Electronic address: mminokenudson@partners.org.
authors: Mari
authors: M
authors: Mino-Kenudson
mesh_terms: D002288:Adenocarcinoma, Mucinous / Q000145:classification / Q000473:pathology / Q000601:surgery; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D021441:Carcinoma, Pancreatic Ductal / Q000145:classification / Q000473:pathology* / Q000601:surgery; D002291:Carcinoma, Papillary / Q000145:classification / Q000473:pathology / Q000601:surgery; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D010183:Pancreatic Ducts / Q000473:pathology* / Q000601:surgery; D010190:Pancreatic Neoplasms / Q000145:classification / Q000473:pathology* / Q000601:surgery