Low-grade appendiceal mucinous neoplasm vs. high-grade appendiceal mucinous neoplasm - similarities, differences, and current management challenges

Sep 23, 2026

Appendiceal mucinous neoplasms are rare and remain difficult to align in terminology, staging, and management with conventional colorectal cancer. This review summarizes evidence on classification, pathology distinctions, clinical behaviour, prognosis, and management of low-grade (LAMN) versus high-grade (HAMN) appendiceal mucinous neoplasms. Both share non-infiltrative growth, but HAMN shows high-grade cytologic atypia and greater association with high-grade peritoneal disease after dissemination. Management should integrate histology with extent, perforation status, peritoneal cellularity, and dissemination pattern rather than cytology alone.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages7

Reading Time18 min

AccessFree to download

Introduction

Evolution of terminology and classification

Clinical distinctions and prognostic implications

Current management challenges

Practical clinical framework for LAMN vs HAMN

Appendiceal mucinous neoplasms are rare tumours whose terminology, staging and management remain difficult to align with conventional colorectal cancer paradigms. Low-grade appendiceal mucinous neoplasm (LAMN) is well established, whereas high-grade appendiceal muci nous neo plasm (HAMN) remains less clearly defined in clinical practice. This review summarises current evidence on the classification, pathological distinction, clinical behaviour, prognosis and management of LAMN and HAMN. Both entities share a non-infiltrative growth pattern, but HAMN is distinguished by high-grade cytologic atypia anda greater association with high-grade peritoneal disease once dissemination occurs. In appendix-confined, nonperforated disease, HAMN seems to behave more like LAMN than invasive adenocarcinoma, so high-grade cytology alone should not be taken asan indication for routine right hemicolectomy. When perforation, extra-appendiceal mucin or peritoneal involvement is present, management should be escalated to specialist multidisciplinary assessment, with surveillance and consideration of cytoreductive surgery with hyperthermic intraperitoneal chemotherapy tailored to disease extent. Management should therefore integrate histology with disease extent, perforation status, peritoneal cellularity and dissemination pattern rather than rely on the cytologic grade alone. Key words: appendiceal neoplasms, low-grade appendiceal mucinous neoplasm, high-grade appendiceal mucinous neoplasm, pseudomyxoma peritonei, cytoreductive surgery. Contemp Oncol (Pozn) 2026; 30 (2): 110–116 DOI: [https://doi.org/10.5114/wo.2026.163813](https://doi.org/10.5114/wo.2026.163813) Review paper Low-grade appendiceal mucinous neoplasm vs. high-grade appendiceal mucinous neoplasm: similarities, differences, and current management challenges Paweł Lesiak1, Bartosz Kapturkiewicz1,2, Tomasz Jastrzębski3,4, Marek Bębenek1,2, Michał Kazanowski1,2 1Department of Surgical Oncology, Lower Silesian Center of Oncology, Pulmonology and Haematology, Wroclaw, Poland 2 Faculty of Medicine, Wroclaw University of Science and Technology, Wroclaw, Poland 3Oncological Surgery Department, PCZ Brzeziny Hospital, Brzeziny, Poland 4Clinic of Gynaecology and Obstetrics, Medical University of Gdansk, Gdansk, Poland Introduction Appendiceal mucinous neoplasms are uncommon tumours whose pathological features and clinical behaviour differ substantially from conventional colorectal adenocarcinoma [1–4] . Their rarity, heterogeneous presentation, and repeated changes in terminology have made cross-study comparison difficult and management uncertain [1–3, 5]. Within this spectrum, low-grade appendiceal mucinous neoplasm (LAMN) is now well-recognised, whereas high-grade appendiceal mucinous neoplasm (HAMN) remains less clearly defined in clinical practice despite increasing diagnostic recognition [1, 3, 6] . Both entities share the non-infiltrative architecture of appendiceal mucinous neoplasia, but HAMN is distinguished by high-grade cytologic atypia; placing it in a biologically ambiguous position between LAMN and invasive mucinous adenocarcinoma [1, 3, 6] . Since its formal recognition in the Peritoneal Surface Oncology Group International (PSOGI) classification and subsequent incorporation into modern staging systems, HAMN has posed persistent clinical uncertainty: how aggressively to stage it, whether extended resection is warranted, and how intensively to follow patients [1, 3, 6, 7] . That uncertainty is compounded by discordance between pathology nomenclature and tumour-node-metastasis based staging, and by the small size of most published HAMN cohorts [2, 6, 7] . Recent evidence has clarified the picture without fully resolving it. Larger contemporary cohorts show that HAMN is more often associated with peritoneal dissemination and higher-grade peritoneal disease than LAMN [6, 8] . Yet in patients with a non-perforated appendix, HAMN outcomes appear closer to those o

FAQs

What similarities do LAMN and HAMN share in growth pattern?

Both entities share a non-infiltrative growth architecture of appendiceal mucinous neoplasia. This common structural pattern is contrasted with differences in cytologic features and disease spread.

How is HAMN distinguished from LAMN in pathology and clinical behaviour?

HAMN is distinguished by high-grade cytologic atypia. It also shows a greater association with high-grade peritoneal disease once dissemination occurs.

Why should high-grade cytology alone not automatically trigger right hemicolectomy?

In appendix-confined, non-perforated disease, HAMN seems to behave more like LAMN than invasive adenocarcinoma. Therefore, cytology alone should not be treated as a routine indication for right hemicolectomy.

Sep 23, 2026

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