How Does One Treat Lesion On Sternum After Having Undergone Prostatectomy Previously?

My husband is 77 years old, had prostatectomy 15 years ago, Psa has been .0002 for years.
2 months ago, he had vasovagal attack following food poisoning and collapsed in the bathroom landing sideways. He had X-ray taken but no signs of damage to his bones. After a month, he still had pain in his back which I thought he might have sustained a fracture that was not detected. After a week an x-Ray result came back showing a lytic lesion to his rt 5th rib. A Ct scan has confirmed 2 lytic lesion to his ribs and one on his sternum in front of his heart. All blood results FBC UE, LFT AND BONE PROFILE were all so far normal. A PET scan was done yesterday. If this is likely to be malignant or not, what are we likely to expect? I await for your reply. Thank you.