My Father Who Is 75 Had A Lesion In His

My father who is 75 had a lesion in his voicebox about 4 months ago. Dr. gave him something to take and told him to see him in 4 months. So here we are 4 months later and they went to see the dr. yesterday and the lesion happen to be smaller BUTT the dr. wants him to have a biopsy anyway which would mean he would have to have anesthesia and be treated like a mini surgery. Why would he suggest this now if the lesion got smaller?