Introduction: Anorectal melanoma (ARM) is rare and highly lethal neoplasm. It has a poorer prognosis compared with cutaneous ones. Sentinel lymph node biopsy (SLNB) has become the preferred method of nodal staging method for cutaneous melanoma. The role of SLNB for staging of anal melanoma remains unclear. This study investigates SLN identification and biopsy in patients with ARM.

Methods and patients: We present our experience of patients affected by ARM who underwent to SLNB. Clinical workup included digital rectal examination, anoscopy, rigid proctoscopy, total body (computed tomography) CT scan, pelvic magnetic resonance imaging (MRI), and fludeoxyglucose-18-positron emission tomography-CT (FDG-PET-CT) to obtain an adequate pretreatment staging of the patients. Wide local excision and contemporary SLNB were performed to remove primary neoplasm and detect inguinal lymph node metastases.

Results: In total, five female patients, median age 68 years, were included. All were affected by anal melanoma. Detection rate of SLNB was 100% and scintigraphic migration was unilateral in three patients and bilateral in the other two. Definitive inguinal histological exam revealed unilateral metastases in three patients, bilateral metastases in one case, and the presence of isolated neoplastic cells in the remaining case. SLNB allowed a diagnostic upgrading of inguinal metastases in three of five patients (60%), permitting better staging and further appropriate treatment.

Conclusions: Our experience demonstrates SLN biopsy is a minimally invasive, cost-effective, and rapid procedure for accurately staging patients with clinically occult disease. In fact, SLNB emerges as an appropriate procedural tool to identify patients with occult lymph node metastases who could undergo immune or target therapy, as well as to avoid unnecessary inguinal lymph node dissection for patients who would not benefit.

Keywords: Anal melanoma; Immunotherapy; Local excision; Mucosal melanoma; Sentinel lymph node biopsy.

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