thank you so much for asking your question, I will do my best to help. since it started as what you describe as a pimple, it is highly unlikely that it is a cancer. it sounds much more like a pimple that may have gotten infected. this could be due to an ingrown hair or many other possibilities. it can also be a fungal infection. I think it makes sense to keep it clean and use an antibiotic ointment like neosporin several times a day for a few days. if it resolves, you have nothing to worry about. however, if it gets worse, or does not resolve in a few days, it is very important to see your doctor for an exam just to make sure it isn't something worse. I hope this helps, please let me know if you have any more questions.