Hi, I had gone through your question and understand your concerns. First, this is not sign of cancer and cancer is the last thing to think of. At this area it may indicate several issues and most common are pilonidal cyst or perianal abscesses. These are inflammatory processes in sacral and perianal area usually manifested with pain, redness, swelling, fever and pus discharge. Cellulitis is less common and may be present in sacral area as well. This is mostly caused by beta hemolytic streptoccocus and it necessitates antibiotic treatment with augmentin, or combination of ciprinol+ metronidazole. You should also, apply cold compresses, take nonsteroid painkillers such as ibuprofen 400mg and rest. If there is no improvement within 2 days, you should see doctor and have intravenous antibiotics. In some cases if this persist it would be good to do colonoscopy. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health.