CASE REPORT article
Front. Oncol.
Sec. Surgical Oncology
This article is part of the Research TopicEmergency Surgery for Abdominal Cancer: Challenges and InnovationView all articles
S100-Negative Primary Anorectal Melanoma with Elevated Ki67: A Case for Biology-Driven Radical Resection Despite Early Radiological Staging
Provisionally accepted
- Affiliated Hospital of Hebei University, Baoding, China
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Background: Primary anorectal melanoma (PARM) is a rare and highly aggressive malignancy. Diagnosis is often challenging due to non-specific symptoms and potential S100 negativity on immunohistochemistry (IHC), while optimal surgical management remains debated. Case Presentation: A 67-year-old woman presented with hematochezia, tenesmus, and overflow pseudodiarrhea. Clinical examination and MRI identified a 2.0 cm ulcerated rectal mass, staged as cT2N0. Initial biopsy revealed atypical melanocytic proliferation. Definitive IHC of the resection specimen confirmed melanoma, showing S100 negativity but positivity for HMB45, Melan-A, and SOX10. A notably high Ki67 proliferation index was observed, escalating from 30% in the biopsy to 60% in the resected tumor. Despite the early radiological stage (cT2N0), the high Ki67 index indicated aggressive tumor biology, prompting a multidisciplinary team to recommend abdominoperineal resection (APR). Adjuvant chemotherapy with temozolomide and cisplatin was administered postoperatively. The patient remained disease-free at 24-month follow-up. Conclusion: This case highlights that S100 negativity does not preclude a melanoma diagnosis when supported by other specific melanocytic markers. Furthermore, a markedly elevated Ki67 index may identify biologically aggressive PARM tumors that could benefit from radical resection, even in the context of early radiological staging. Biology-driven surgical decision-making, complemented by adjuvant therapy, may improve outcomes in this high-risk subset of patients, though larger prospective studies are needed for validation.
Keywords: Primary anorectal melanoma, Ki67 proliferation index, Abdominoperineal resection, Immunohistochemistry, S100-negative, Treatment Decision-making
Received: 22 Aug 2025; Accepted: 27 Nov 2025.
Copyright: © 2025 Ren, Xie, Liu, Jin, Ma, Sun and ZHANG. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Meng ZHANG
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