Background: Anal metastasis originating from colorectal carcinoma is a rare occurrence that severely affects the patient's quality of life. No standardized effective therapeutic strategy exists. Objective: Our aim was to examine clinicopathologic characteristics and outcome of patients with anal metastasis of colorectal origin, directing particular attention to underlying mechanisms of metastasis in relation to potential treatment strategies. Setting and Patients: We identified patients with anal metastasis of colorectal origin by reviewing medical records of patients treated for colorectal cancer in a tertiary teaching hospital in the Osaka region of Japan between 2002 and 2009, and by searching the PubMed and Japanese Ichushi databases for patients reported in the literature. Main Outcome Measures: Clinical and pathologic variables were examined, including location, depth, and lymph node status of the primary colorectal tumor; mode, timing, site, and symptoms of metastases; as well as treatment and prognosis. The mode of metastasis was classified as either intraluminal or lymphovascular on the basis of clinical history of anal disease and/or histologic analysis of a resected specimen. Results: Of 851 patients with primary colorectal cancer treated at our institution, 6 patients (0.7%; 95% CI, 0.1- 1.3%) had anal metastases, and 38 patients with anal metastases of colorectal origin were identified in the literature; 43 patients could be analyzed. The primary lesion was located in the left colon in all patients. The metastatic mechanism was identified as intraluminal in 35 patients and lymphovascular in 8 patients. Local recurrence after local resection was not reported in any patient with intraluminal metastasis, but was found in 3 patients with lymphovascular metastasis, although all 3 had undergone wide resection. Limitations: The study was observational in nature and included a small number of patients. Conclusions: Treatment strategies for anal metastasis of colorectal carcinoma origin should consider the mechanism of metastasis. Patients with suspected lymphovascular metastasis should undergo radical resection beyond the primary and metastatic anal tumor to eradicate remnant cancer cells, together with preoperative chemoradiation therapy.
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