I also had something on the upper lobe of my right lung 'light up' in the PET/CT just prior to beginning treatment. My RO was sure it was early lung cancer and scheduled me for a needle biopsy (lung puncture through the chest). Two weeks later when they did the contrast CT preparing for the lung puncture, it was gone! There was nothing to biopsy. It was some sort of 'inflammatory' process. Not everything that 'lights up' is cancer.