A controversial area and I refer you to the references.
However for practical purposes LAMN (low grade appendiceal mucinous neoplasms) are a distinct subset of appendiceal mucinous tumours that lack usual forms of destructive invasion into the appendiceal wall. Histologically the normal appendiceal mucosa is replaced with a villiform mucinous epithelial proliferation.
Despite the bland histology of the mucinous epithelium these have the propensity to spread to the peritoneum and ovaries, frequently progressing to the clinical syndrome known as pseudomyxoma peritonei and often results in the demise of the patient. PP results in death of 50% of patients from bowel obstruction.
Appendiceal mucinous neoplasms. Controversial Issues. Misdraji J., Arch Pathol Lab Med – Vol 134, June 2010