Hello. Very Good evening. I'm Dr.Yogesh Kr Sharma. As per history given, every tumour or lump  is not a cancer. First of all we have to get a diagnosis. You should go for MRI Knee without contrast. And also there is a pathological test known as FNAC ( fine needle aspiration cytology).  In which some fluid is taken from the tumour of Knee and send for examination for its nature. After the reports, kindly come to practo chat for your treatment part and counseling. Regards