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N staging of anal cancer according to the locations of involved regional lymph nodes. N1 anal cancers have metastases in perianorectal lymph nodes only. N2 anal cancers have metastases in unilateral internal iliac and/or inguinal lymph nodes. N3 anal cancers have metastases in mesorectal and internal iliac and/or inguinal nodes or in bilateral internal iliac and/or inguinal nodes. Blue-green = involved lymph nodes, red and blue = external and internal iliac arteries and veins.
