<s>[INST] I have a swollen bump on my lower back that has become painful over the past week. There is a dark spot in the middle and it was previously considered a small, benign collection of fluid, however, it has recently increased in size and is now red, and it it painful to cover it. What could this be? [/INST] Hi, dairy have gone through your question. I can understand your concern. You may have some soft tissue tumor like lipoma, neurofibroma or dermatofibroma.  Or some benign cyst like sebaceous cyst.  You should go for fine needle aspiration cytology or biopsy of that lump. It will give you exact diagnosis. Then you should take treatment accordingly. Hope I have answered your question, if you have doubt then I will be happy to answer. Thanks for using Chat Doctor. Wish you a very good health. </s>