I had biopsies in the lymph nodes, FNAB under ultrasound guidance, that was smaller than 1cm, actually my last was 3mm x 7mm that proved positive for cancer, not saying yours is, but like all cancer, it's best to get at early. For any suspicion on the PET/CT, mainly lymph's, my ENT's, RO, never hesitated to rule out cancer.
Good luck.