Ganglion Impar Neurolysis for the Improvement of Radiation-Induced Pain During Localized Anal or Perianal Skin Cancer Treatment

This study is testing a nerve block procedure called ganglion impar neurolysis — where a pain-blocking agent is injected near a nerve cluster at the base of the spine — to reduce severe pain caused by radiation treatment for anal or perianal skin cancer. Radiation-induced pain in this area can be debilitating and hard to manage with standard pain medicines. **You may be eligible if...** - You have been diagnosed with anal cancer or perianal skin cancer - You have started or are about to start chemotherapy and radiation treatment - You are consistently rating your pain at 5 or above out of 10, or your pain is significantly interfering with daily life - You are 18 years or older - You are in reasonable health (ECOG 0-2) with life expectancy over 12 months - HIV-positive individuals and people with immunocompromised status are also eligible **You may NOT be eligible if...** - Your white blood cell count is too low (absolute neutrophil count below 1500) - Your platelet count is below 80,000 Talk to your doctor to see if this trial is right for you.