What is a low-grade appendiceal mucinous neoplasm (LAMN)?

Low-Grade Appendiceal Mucinous Neoplasm (LAMN): Definition and Management

Low-grade appendiceal mucinous neoplasm (LAMN) is a precursor lesion for pseudomyxoma peritonei that requires appropriate surgical management based on tumor characteristics to prevent peritoneal dissemination and recurrence. 1

Definition and Pathological Features

• LAMN is characterized as a mass-forming pre-invasive neoplasm that grows within the appendix with mucinous epithelium showing low-grade dysplasia 2
• These tumors display simple glandular architecture with elongated and crowded neoplastic cells that maintain polarity with respect to the basement membrane 2
• LAMN is distinguished from high-grade appendiceal mucinous neoplasms by the absence of pronounced nuclear atypia and loss of epithelial cell nuclear polarity 2
• Two distinct subtypes have been identified: Type I (disease confined to the appendiceal lumen) and Type II (mucin and/or neoplastic epithelium in the appendiceal submucosa, wall, and/or periappendiceal tissue) 3

Clinical Presentation and Diagnosis

• Most LAMNs are identified incidentally during appendectomy performed for suspected appendicitis or right iliac fossa pain 3, 4
• The average age at presentation is approximately 60 years with no clear gender predilection 4
• LAMNs can be asymptomatic but may rupture and seed mucin and neoplastic epithelium into the peritoneum, causing pseudomyxoma peritonei (PMP) 1
• Microscopic examination may detect mucin and/or mucinous epithelium herniating into the appendiceal wall even without obvious perforation 4

Risk Factors for Progression

• T stage, appendix perforation, presence of acellular mucin on the serosa, and surgical margins are risk factors for the development of pseudomyxoma peritonei 1
• Type II lesions have pathological features that indicate increased risk for dissemination 3
• Mucin, cells, or both outside the appendix are observed in approximately 58.5% of cases 5
• Appendiceal rupture occurs in about 51.2% of cases and is a significant risk factor for peritoneal spread 5

Management Recommendations

• For LAMN confined to the appendix (Type I):

  • Simple appendectomy is sufficient for well-differentiated tumors <1 cm with no adverse features 6
  • A watch-and-wait surveillance policy with serial measurement of tumor markers and CT imaging is appropriate 3

• For LAMN with high-risk features (Type II):

  • Right hemicolectomy is indicated for tumors ≥2 cm, even without obvious malignant features 6
  • Further resection (right hemicolectomy) should be considered if the tumor breaches the serosal surface, invades the mesoappendix by more than 3 mm, or is located at the base of the appendix 6
  • When LAMN involves the appendiceal base, partial cecectomy is preferred by most specialists (67%) over right hemicolectomy (33%) 7

• For LAMN with peritoneal spread:

  • Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (HIPEC) is recommended for T4b disease or when mucinous implants contain tumor cells 1, 7
  • For limited peritoneal spread (confined to pelvis and right lower quadrant), macroscopically complete surgery followed by surveillance may be appropriate 5

Surveillance Recommendations

• For patients with completely resected LAMN without high-risk features:

  • Follow-up examinations as clinically indicated, with some institutions suggesting examination at 1 year post-appendectomy and then with decreasing frequency 8

• For larger tumors or those with adverse features:

  • Follow-up every 3-12 months for up to 10 years 6
  • Perform multiphasic CT or MRI (abdominal/pelvic) during follow-up 6
  • Consider chromogranin A as a tumor marker, particularly for neuroendocrine components 6, 8

Prognosis

• When LAMN is treated surgically with resection of the primary site in early stage disease, there is an excellent prognosis 4
• The 5-year recurrence-free survival rate is approximately 95.1% for radically resected LAMN, even with limited peritoneal spread 5
• Recurrence typically occurs within 2 years of initial surgery in the small percentage of patients who experience disease progression 5

Common Pitfalls to Avoid

• Performing right hemicolectomy for all LAMNs is unnecessary and represents overtreatment for confined disease 7
• Underestimating the risk of peritoneal spread in cases with high-risk features can lead to inadequate management 1
• Failing to thoroughly examine the entire specimen for evidence of wall invasion or perforation may miss important prognostic information 4
• Not considering the presence of acellular mucin on the serosa as a risk factor for recurrence 1